Dick: "Goran, I must admit, I'm getting rather comfortable with my Baritone now".

Sounds comforting in double meaning but there obviously are a couple of reservations...

Dick: "I only used the Thumb Straps"

Magnificent! You have become Honorary Member of the 4fingerSociety*** and may apply for membership of the ScrapthefingerplateSociety*** as well...

Dick:"The only trouble was, when I stood up I couldn't walk because my leg had gone to sleep! ;-)"

Hmm...you have broken one of the golden rules of ergonomics and got an automatic punishment. I use one of these adjustable (one-)foot stools for classical guitarplaying to lift one thigh a little when sitting for a longer time

Dick: ". perhaps what I really need is an "ergonomic" CHAIR! :-)"

That really is an interesting topic itself.Leaning back comfortably and playing in an armchair is no trouble - arranging the music stand may be tricky however - but there are reading-tables on the market that serve quite well.
(Otherwise...hanging the instrument up in straps from the ceiling while staying in bed is the ultimate way of doing our stuff with minimal effort. It is also an excellent method demonstrating that the end area is the cause of differences in playing effort between small and big concertinas...)
Goran