Be a Beast Rider Cavalier and you can basically have the same flavor as (and similar crunch to) a paladin.
Ditto a animal domain cleric - but the crunch is even further off.
Your question about will the animal be survivable with 1 CL behind for the AC? Definitely. Also see how your DM rules on robes of Arcane Heritage - some feel they increase your level for eldritch heritage, some don't.
Personally I find that my DM's hardly ever target your mount unless you're not on them. YMMV, of course, but that's my experience. I have a 14th level mounted character (actually a nature oracle) and I can count the mounted combat ride checks I've had to roll to avoid attacks on both hands.
Alternately, take a look at the Half-Orc feat Beast Rider. Gives you some alternate choices and +2 effective druid levels for an AC. Needs character level 7, but I'd think you can convince your DM to use that feat (or use it as a baseline for a similar feat for other races) to apply to lion. Lions certainly aren't as powerful as some of those creatures allowed.
Why not ask the GM to simply allow your "divine bond" animal to be a lion? I personally find the limitation to "horse/camel" to be kinda silly, but that's me. There are clauses that say something along the lines of "any other animal at GM discretion", so your GM might allow it? Will have to small at the beginning though (since it starts medium).
+1 to williamoak's comment
This mount is usually a heavy horse (for a Medium paladin) or a pony (for a Small paladin), although more exotic mounts, such as a boar, camel, or dog are also suitable. This mount functions as a druid's animal companion, using the paladin's level as her effective druid level.
more exotic mounts are built right into the ability- they need to be mounts though (a quadruped that's the right size: large-huge for a medium pally), a lion meets that requirement starting at 7th level (when it becomes large) so just talk to your GM about why you want to do it, what makes it suitable for your guy/concept and see what he says.
if that doesn't work, talk to him/her about using the sylvan bloodline... personally i don't allow it (for 2 reasons- there's no mechanic for taking wildbloodline features with eldritch heritage, and the companion is the arcana that also replaces the 1st level power), but if you're willing to invest a bunch of feats to minorly improve an ability you already have that's tough to say no to.
Oh my, that's an unfortunate typo in the OP.
See if you can get Magical Knack to apply to the Eldritch Heritage. That plus Boon Companion will bring it to full CL, although the overflow will be wasted and CL-1 is perfectly survivable. It's still worth trying unless you really, really need two other traits.
The Beast Rider feat allow orcs and half-orcs to get additional choices.
I'd just talk to your GM about getting a feat, that let you choose a lion for your bonded mount.
the only thing your GM might be worried about is pounce, but yeah, it's not too much of a stretch.
Paladin Riding a Lion.
MTG FTW!
Anywho, you could always RP it. If you have ranks in Handle Animal, which I believe it's a class skill for pallies, you could go on a quest to tame a mighty mount. I've noticed most dms are willing to try something if you can make a story out of it.