Sounds pretty much like typical North sea conditons to me. I use a shorty in months after june. Before that I either use a good wetsuit or since 2 years a drysuit in the months april to june when the water temp is rising from 5-6 degreee celsius to about 15-20 degrees. Having said that the first 3 years I had a 15 year old worn down wetsuit of 2.5 mm thickness and a spraytop (that is nice to have) and done it like that. Arguably I was in my 20's then and could stand a little cold during the first months of the season. a new 3mm (preferable with 4 mm on the chest) is the better option together with a relative thick spraytop. I never really liked drysuit for long periods although the magic marine drysuits are the best I know and I bought one of these. But like I said I only wear that one in the first months and on longer trips.
Now I do understand why you adviced the Wave , Mary. The explanation is very helpful in underscoring your advice.
Still, I think a boat a little more powered up is the way to go. I need to check up on the Baltic sea windconditions but I really don't expect it to be haunted with sudden gail force storms. After all it is totally enclosed by landmass and quite away from the Atlantic oceans. If anything most storms (arguable coming from the atlantic) will have lost alot of power of the land. T55 must correct me if I'm wrong
Wouter