I suggest you fly. Flying with kids - especially when they're not fully mobile - is really really easy. My son - also 9 months - has flown to Europe and back, to Seattle, to San Diego, and to NH (he's very well traveled, yes). We have always taken him as a lap child and for most flights have flown Southwest, which is nice because you can almost always get a row of 3 seats with an empty one. (Plus, you get to preboard).
Here are some suggestions:
1. If you are flying and it is going to run into his nap time, make sure you are seated farther back in the plane. Most families/kids sit in the front and if there are any number of them on board it will never be quiet enough for him to sleep.
2. The altitude thing is no big deal - just make sure that he swallows whenever you swallow to pop your ears. So either nurse/bottle feed him at take off/descent, or even just giving him a little snack or some juice will take care of this.
3. You can take a carseat on (you'll have to pay for a seat then, but at a reduced price usually) but if your son is anything like mine, he'd rather be held by you than sitting next to you. Still, it might be nice for naps. You need to put the carseat all the way in by the window if you use one.
As for entertainment, I would just bring a few of his favorite toys and books. And, if it were me, I would NOT ship any of his toys down to FL with you. There are lots of things to entertain a baby - pots and pans, tupperware, etc. No need to hassle with anything bulkier. Just bring a blanket for him to roll around on and a pack N Play (though honestly, when we travel our son frequently ends up in bed with us since he doesn't sleep well away from home).