I think you go smaller to a certain extent. Smaller also means less stable. There is a tradeoff at which point lack of stability becomes harder to sail than complexity. Larger boats are more complex. Smaller boats become unstable. I would find that 22-25 ft boat with fewer systems that sails well single handed. Then always sail with crew. Not hired. Face it. Few people can hire crew. However, willing sailors can always be found. Marinas are full of friendly people. Also, sail on other people's boats. Invite people, and they will reciprocate. Rule: if someone invites you... reciprocate with an invitation!
Next, accomodate limits: reaction time, strength, sight, and hearing all fade with age. You know what? Bladder capacity also diminishes with age! Ask people to sail for shorter periods or if they will mind you using the head. ALWAYS ask if you can use the head on someone's boat!
Maybe move to a slip that is on a T to facilitate easier docking. Inform others of a sail plan, so friends can be on hand for docking help.
The key is to accomodate limits in order to keep active and sailing. People around us will help.
I agree that continuing to do weight-bearing exercise is important for maintaining strength and skeletal integrity and support. We should all be in the gym. All of us.
Think your way through every step, every facet and factor. Simplify each one to accomodate limits.
You may not even need to own a boat!