I've latley been thinking quite heavily on this topic.
and I thought of a strange solution, the problem with depth is pressure?
Using something so simple.
If water pressure is the problem eliminate it entirely using heated evaporation
Imagine a Metal Chassis, a Gridded layer of Thermal coiling.
another layer of metal that is cooled.
it wouldn't have to be heavy, infact the lighter the better.
less weight would be ideal for the most mobility possible
If it does Null the pressure it would be constantly evaporating a layer of water
Visibility wouldn't be possible due too the steam. I suggest no windows, only cameras too see.