I have the exact same problem. 6'0 (183.5 cm) height, 160lbs (72kgs), and a long torso. Mediums and even smalls are ideal for my shoulders and chest but it's a crapshoot if they will keep my belly button covered through a normal range of motion. I don't want to bare it and can't imagine anyone wants to see it.

Tentrees, Fox and Prana are the brands I've found that consistently fit my upper body.