If you only have one deco bottle, why don't you have it chest and hip clipped? Even if over a stage?
When I dive with 50% in an 80 al and 100% in a 40 al in a cave, they get dropped going in. Coming out, pickup at 70' and clip off the 50% and breath it on the way out. At 20', pickup the 40 and clip it over the 80 and switch. Both are clipped and controlled.
In an open water trimix dive where I have a bottom stage, 50% and 100% or a cave dive where I have 2 travel stages and 2 deco bottles, something gets nose clipped to the hip, maybe with a leash. At the end of the dive, I don't know how to keep them all 'down'. In the cave with trimix travel stages on a scooter I can keep the stages clipped at two points and streamlined. By the time I get back to my 50% and the stages are pretty light, I have enough space in the cave that I can 'float' the stages and streamline the deco gasses as I pick them up.
I am a left side guy. I tried the right/left but found it more complicated for what ever reason. But, if right/left, I can keep two bottles clipped at two points on each side.
Now I am starting into SM and am using the SM stage top mount method and kits. Haven't figured out all of that yet but the theory is stages top mounted and deco bottom mount 'hanging' In the case of two stages, one top mounted on each side, so, I'd have bottom mounted deco bottles on the left. But, I haven't had all that on yet. I've dropped a 40 going in and had one stage with a scooter and that's as much as I tried to date SM.