Here's another alternative if you have the financial resources ... Go the route of Charles Daellenbach.
He's in his mid-70s and still running around on stage and doing gymnastics with his (relatively small size) CC tuba. But he's got a CARBON FIBER bell on it!! He also uses a Kelly plastic mouthpiece, but I doubt it's part of his weight reduction approach.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)