Are you allowed to take your own inflatables to the pool?
We spent most time at the turtle pond pool. People had small child-sized inflatables, beach balls, and pool noodles. We didn't see anything larger, and I suspect that an adult sized inflatable would not be appreciated if there are a bunch of people in the pool. 2 pool noodles does the trick for relaxing though
Heather's answer is good. I was just thinking of the Sand Castle pool, which always has lifeguards. No flotation devices are permitted.
However, in the other 3 "quiet pools," where there are no lifeguards, you can probably bring in your own inflatables.
Get an answer from Disney's Old Key West Resort staff and past guests.