shorter boots are one option - I always recommend open heel + boots rather than full foot fins but there is a certain amount of personal preference involved. Booties reduce problems associated with wandering barefoot over hot sand or rocks or broken coral on the beach etc.
If your feet are only a bit floaty, you can get over this with simple practice and modifying your finning technique a little or re-distributing your weight to bring your legs down a little to compensate. If you're wearing a lot of weights in an integrated weight-pocket BCD, for example, there is a tendency to force the body into a head-down, feet up position, for example, and so shifting some of the weight to a belt can help. How you do all this is a little bit down to you and a little bit down to trial and error, to be honest. There are also ankle weights for super-floaty feet but I reckon (without knowing the exact circumstances) that you don't need these.
In terms of fins, the avanti quattro are awesome, basic, paddle fins. You could look at heavier fins made of vulcanised rubber such as jetfins (which I personally don't like), but I always recommend, as far as possible, that you try before you buy. To save yourself some money in the first instance, see if you can overcome the problem by experimenting with your finning technique, body and weight position. It's impossible for me (or anybody) to give you a super-accurate answer without seeing you in the water with exactly what dear you are wearing (and also what you look like, to be honest).
Hope that helps a little
Cheers
C.