Throwing in a Witch, a Bard, or (if the Ranger or Cleric isn't planning to be a front-liner) a Magus can give you the control element while adding enough else to the PC to make it interesting.
What kind of off-the-wall concept are you considering?
Witch. Healing really wouldn't be an issue for that party. If the cleric is a nature cleric of some sort, would work really great. Witches can be fun, regardless.
You can make a Witch that plays like a Native American shaman if you want (with a brujo feel, if you're so inclined); or a Tien sensei type; or a Ustalavic gypsy; and so forth.
Now I want to play a halfling witch with a gypsy theme.
I assume you mean you want to have a balanced party. Is the alchemist going to attack from range with bombs? Is the cleric going to be a buff tank or a combat spellcaster or a healer, etc? What fighting style is the ranger going to use? Do you have anyone using an archetype that can find and disable traps? Is that an issue in the campaign you're running?
What is it that you want to play?
Witches are strong, but everyone that I've talked to in my group that's played them, and the one time I played one, I was incredibly bored with it within a few sessions.
If I was going to roll up a character for a game tomorrow, I'd roll up a bard / cavalier / battle herald that uses a whip for disarming and tripping. You can have your pick of left over melee weapons for actual damage dealing, and could even go into 2WF, though I'd concentrate on Str and Cha, personally. This gives you tons of options, you can be effective in many ways, and fills a role your party doesn't necessarily have at the moment. Several, actually, including party face and heavy support, with some limited battlefield control.