If you don't mind going to a larger bore, then an American-style bell-front euphonium might be just the thing. Here's a very nice Conn (one of the best brands):
http://www.ebay.com/itm/CONN-BARITON...-/221581558210
Or here is a nice King in similar format:
http://www.ebay.com/itm/KING-BARITON...-/221558008387
These are the two brands I played during my public school days. Both are very easy on the body (much more than the horn I now play). The Conn is just a bit lighter usually (which might make it easier to hold up), but the King is built with a longer body (which might make it easier to rest on your leg).
The larger mouthpiece of the euphonium (the horns above are often called "baritone horns") doesn't require as much chop pressure to play high, and that might help save your neck.