You mentioned Fboats earlier. The main problem with sailing an Fboat is the lack of available/reliable crew members. If you really plan on getting one you need to sail on several to determine which one you like. For me it was the F25c for a friend it was the F28R. If you make yourself available you could probably crew on some Fboat at least once a week. You might try the nationals web site for crew positions available. My first sail on a F31 was at the 2001 nationals. There were 67 Fboats that year. Try the link below... Theres usally a free ride somewhere at these events.
As far as bad knees; steering or sail triming would be the best for your wife. Also wives are welcome crew members as well especially if they can cook
fair winds,
thom
2001 Nationals