Any homebrew rule suggestions for underwater adventuring?

[mardaddy]

Home group I am DMing will be sporadically having to deal with adventuring underwater in an ocean bay for the next six levels (some sandbox, eh?)

Does anyone have homebrew / houserules they use to augment RAW that they could suggest?

[ronald paris]

not homebrew but check cerulean seas setting plenty of stuff there

[mardaddy]

I am already buying it after the new year.

Bought Aquatic Adventures and looking at Kobold Presses Sunken Empires also, but wanted to see if anyone has done any homebrew, different approaches. "Casting the net wide," so to speak.

(see what I did there..?)

[Goth Guru]

On another topic someone suggested map stacking. Similar to airborne combat.