My best suggestion would be to check out the complete warrior for there bear warrior class or the forgotten realms for their shapechanging warrior types,I think they are in and around rasheman.
I dont know why you want to limit the magic in the game but might I suggest the adept class, they arent very powerfull and they can heal but not as much as a cleric. Your party is going to need some survivabilty.
If you really want to make magic items rare get ahold of a second edition dmg and use those rules. Even a simple potion of healing was a major undertaking at times and really enforce the component rules.
Good luck.
Check out what I did with a low-magic campaign in my (now free) The New Argonauts book. All the magic items in the game come from taking a special feat to make thematically-appropriate items out of dead monster parts.
High-level D&D relies tremendously on the existence of magic items. Lots of them. To the point where it just breaks entirely too much to even try it. It fundamentally shatters the basic premises of the game, to the point where the game pretty much ceases to function. 3.5 is absolutely not a low-magic game, and oftentimes it's easier to go to an entirely different system than try and use 3.5 for low-magic unless you want to stick to level 3. You're pretty much ripping out the entire economy; loot is one of the primary aspects of the game, and you're rendering it useless by removing the one thing it's actually spent on (and note, making magic items ten times more expensive when they do find them is the same as giving the party a tenth of the loot they're supposed to get). The mechanical difference is no different than if you were to say having hundreds of hit points is unrealistic, so the PCs just aren't going to get any hit points past level 1.
If you want a campaign that's low on magic items, I don't suggest going beyond level 3. Ever. Even E6 is pushing it.
Alternately, give the effects of magic items explained through other means. Rather than the Fighter getting, say, four thousand gold for killing the dragon that he then goes and spends to buy +2 gloves of strength that make him stronger, the Fighter instead gets 4,000 'awesome' for killing the dragon, that he can burn to get +2 strength because he's just that strong. You have a world without a whole lot of magic items without screwing over the players or gutting the entire game. Even then, it's a bad idea to go past level 8 or 10 that way. E6 is still a better idea here.
As for shape-changing classes? Most of them are higher-level and PrCs. Wild Shape doesn't really come into fruition until level 8 or so, and the shapeshifting PrCs rarely even start until level 6, minimum. Meaning they're all pretty much out of reach.
For a most shape-shifty class, I suggest looking into some of the weirder magic in the game. Magic of Incarnum and Tome of Magic. Specifically, the Totemist and the Binder. They may take some refluffing and revision, but they can easily be adapted to transformation.
The Totemist uses soulmelds (essentially phantom magic items) that allow them to take on various aspects of magical beasts (the creature type that forms the core of the class). One of their signature features allows them to bind melds to gain certain aspects. Like, say, binding the Displacer Mantle to gain two tentacle attacks, as a displacer beast.
It wouldn't be too terribly difficult (particularly if you run the game in E6) to remake the class so that melds center around animals, rather than magical beasts, and the transformation is more substantial. For example, you could make the Tiger Pelt soulmeld, that grants a bonus to stealth, and when bound gives two claws and a bite. Perhaps the more essentia (floating points that boost the soulmelds) you invest, the more tiger-like you become.
The Binder is written as a pact-making class. Essentially, they allow themselves to be possessed by various 'vestiges' (essentially nigh-godlike spirits) to gain various abilities. Like, one of the low-level ones allows you to summon a suit of full plate, trade places with your allies, and some small damage reduction that's bypassed by piercing damage. Also, when making the pact, you have to make a charisma check against a DC dependent on the vestige. If you fail, you still get all their powers, but they have some strong influence over you. Some quirk of their personality takes hold. They can even force some actions from the Binder. For example, the vestige that grants the armor? He's headstrong and bold, and if they make a bad pact with him (meaning they failed the charisma check that morning), you may not be able to retreat from battle because of his influence. And finally, there's the 'sign.' If you bind armor dude, there's an arrow sticking out of your body somewhere. Another makes you grow great, big ram horns. Another makes you constantly shed tears. Binders do get the ability to suppress these signs, but only if they make a good pact (meaning they passed the charisma check), otherwise, they're stuck with it (though some signs can be hidden).
Now, for adapting the Binder, you have to work with your players to create more animalistic vestiges, based off of the existing ones. The hawk vestige may have a sign of hawk-like eyes, and give you the ability to turn into a bird and fly, and bonuses to your detection skills, or some such. The bat vestige may give you short-range blindsense and a sonic attack (and the ability to turn into a bat, of course). The tiger vestige, of course, gives you some stealth boosts, maybe pounce, and the ability to turn into a tiger with its myriad natural attacks (however, I suggest working the tiger form in a manner more like Pathfinder polymorph or Shapeshift variant Druid, so that base stats actually matter, and a very strong Binder becomes an even stronger tiger, rather than rendering strength/dexterity irrelevant and completely overridden by the alternate form). Some animal vestiges may have more interesting abilities; maybe a hypnotism effect for the snake vestige. Work with your players to come up with cool stuff, but the class can be a good base to work off of.