I'm not going to say anything about warmth, because that is entirely individual, and had been beaten to death on Scubaboard. I would assume your shop provides shorties, or whatever for the pool sessions, and wetsuits for the OW checkout dives (if not, screw-'em). I bought my 7 mil farmer john wetsuit right after certification. It will suffice one way or another for dives within a wide range of temperatures (recent thread). I had no problem using the shop stuff for both the pool and ocean checkouts. Of course, it was about 10-20 post cert. dives when I was really "dialed in" as they say on my buoyancy. I wouldn't mess with buying your own wetsuit for the pool when a shorty will do, and is less to deal with, especially weight-wise. There is enough to deal with learning all the skills first. IMO buoyancy/trim isn't rocket science once you're weighted properly, and all that means is a proper weight check. Others may disagree.