If you are going to get a 7mm you might look for one that has some form of wrist and ankle seal. I dive a Bare Velocity 7mm with a 5/3 hooded vest into the low 50s (F) and that works OK for me. The suit has mid-forearm and mid-calf seals that look pretty anemic, but do seem to help. I think Piranha sells an inexpensive 7mm with wrist and ankle gaskets, and I think the Mares Flexa has wrist and ankle seals. The hooded vest is key -- helps keep that "ice down your back" feeling to a minimum. Past that there are semi-drys -- and people seem to like the Hollis Neotek, though there are many other choices too.
I think a lot depends on the air temperature too. If it is a nice day outside and you can warm up after the first dive, the second dive is OK. If you're cold before you get in the water, though, it will be miserable. (I don't dive if it is cold outside.)
A drysuit is probably in my future -- but, for now, I want to spend more time in the water than fixing my suit.