I've discovered that (not using enchantments or turtle helmets or anything) being underwater in survival is buggy
If you want to build this way, expect to lose all your levels constantly lol.
The CON: Sometimes you can't get into an air pocket or when you do, you still can't breath. I think this is more related to the door mechanic, creating an actual air pocket accessible without a door (such as in a ceiling) maybe will solve this. Technically my base is big enough that I can remove the doors and the water won't fill the whole tunnel, so maybe I'll do that and stop building an "air lock".
That doorless solution is also good for mobs...which can bum rush you as you try to get through a glitchy door.
The PRO: you can build this entire base with stone aged tools rather easily lol.
Also, lighting for when working underwater can be achieved by a door, and a block on top of an empty space. Placing a torch in the empty space clears the water under that block and lets the torch remain.
I just learned you can use dried kelp blocks as fuel, so I need to mine less. I have been mining looking for diamonds, since the sea floor sits about y=30, and my tree farm sits about y=14, but I have found NO diamonds. Perhaps its the biome?
There's a huge cave complex the base is built into, so that's cool.
Still using no enchantments or turtle helmets so the base is entirely built with the excruciating use of doors lol.
Digging one block down to the side at the very start of a tunnel will keep the water from flowing any further down the tunnel.
If you dig out at the floor level and down then you won't get sucked out of the tunnel into the "sumphole".
A 1X2 tunnel just 2 blocks long will have an airspace at head height at the end for a torch and breathing without "wasting" a door or getting stuck on it.
Diamond ore is completely unaffected by biome.
Emerald ore and surface gold in Badlands are, I believe, the only ores that are affected by biome.
Are you mining deep enough?
You should be no higher than Y = 11, some people like to be higher so they have a layer of rock above the lava lakes but the amounts of diamond ore tapers off then, also having the surface you walk on level with the top of the lava means you can pour water over it and keep going, also if you miss it and fall in you have a chance to climb out.
Personally I mine at Y=5, just on top of the highest bedrock blocks, but I'm a weirdo that enjoys mining through lava and obsidian.
I'm mainly using lava for fuel.
It's plentiful, just gets in the way otherwise and my mining trips are often long enough that I can use 2 lava buckets in a furnace with hoppers on top and bottom, sometimes 2 furnaces with 2 lava buckets each.
Or, have you considered using signs instead of doors for your airlocks?
I've gotten so used to my "sumpholes" that I completely forgot about using signs to control water.
They no longer work for removing source blocks of course but they still stop flowing water, so 2 signs on the wall at the beginning of a tunnel will keep the water out completely, and without annoying currents.
Or 4 signs for a 2 wide tunnel.
You no longer seem to be able to run into signs so hopefully you wouldn't get hung up on them like you do with doors.
I've not had any of this "buggy" behavior when underwater. Prior to conduits there were lots of tricks to breathe underwater (signs, buckets, torches, sugar-cane), some of which no longer work, but now we have conduits. Bubble columns are another option in recent versions. Pretty sure signs still work, but you have to place them dry (not in a water block).