If you're on a budget look at the suits from Bare. The Nexgen suit might be what you're looking for.
The shell/neoprene thing has been discussed a lot. A quick summary is this:
Thick neoprene (7mm) : very buoyant, rugged, bad buoyancy qualities
Crushed neoprene (2-4mm): still surprisingly buoyant, extremely tough, adequate buoyancy characteristics.
Shell suits (trilaminat etc): no insulation = thick undersuit needed, neutrally buoyant, relatively more prone to develop leaks than neoprene suits, excellent buoyancy characteristics.
General consensus is to steer away from thick neoprene suits. Most divers prefer the buoyancy characteristics of the shell suits. I personally have had both shell and crushed neoprene suits and I think either of these are perfectly ok.
R..