So anyway. As it is with anything in life, in the end this is going to come down to your personal choice, which I'd suggest you make after demo-ing a few different racquets including the ones you are interested in.
And.. out of curiosity, how old are you? Not to be rude or anything, 88lbs.. 5'6.. is that even healthy? I guess you are one person who doesn't have to worry about the fat they put into today's fast foods!
So anyway, simply put, bigger the headsize, greater the sweetspot. Easier to hit shots. The racquet also adds a lot more power into your shots because of the larger stringbed unless you have a ridiculously high tension.
Smaller the headsize, smaller the sweetspot - this is where you get your wild balls. It takes a while to get used to, I'd say its a little bit more difficult to get used to a smaller headsize coming from a larger one. But its well worth it if you are serious about it. The smaller stringbed is supposed to give you a better directional control on the ball but takes away some of the power.
Those are the two main distinctions, if I had to point out just two. Now a midplus is still a pretty adequate sweetspot and definitely the first kind of smaller headsize you should go to. Midplus would be around 97-104 sq.inch .. around there. And if you are in the process of developing your game I think you'll get used to it in no time, not a big deal at all. You said you can't hit hard. Now thats something that your current racquet should give you an edge in.
In general if you can't hit hard with a 110 sqinch racquet, you might feel even less powerful with a smaller head size. So you know. But again, hard is relative. If you aren't hitting hard with your racquet then I'll say there's a lot you can work on with your technique. No racquet can help you hit with more power than the one you are currently using, so it has to be all technique - and definitely strength. Ultimately the power comes from you, you need to have powerful legs, torso and back. Again, I can't comment on that for you but from your weight, I don't know how much power you are getting. Even on the ATP tour, you'll see the "lighter" guys get outhit frequently and they can't provide too much power for long periods of time
Give us some more details, because from what it sounds like, you are a beginning player and the first and foremost things you should be developing are your strokes and techniques and such. Racquet choice is really very unimportant right now. And if you had to chose a racquet to start off with, I'd definitely go with a mid or midplus as its much more convenient to develop a game in that kind of a racquet and then if need be switch to a smaller head or larger one depending on the game you develop. Right now, IF yo are a beginner, it really makes no sense to judge how hard you are hitting and connect it with your racquet.