Just in case ppl aren't aware the 3 Fused Vitality offered by Depthdiver Tu'nakit can be purchased on a weekly basis.
Three dives of 20000 points will net (ahem) you enough pearls to purchase them all. Getting more points per dive isn't worth it.
I've got all the achievements that get items/boosts now and can safely say gathering the Sunken and Ancient Relics is the easiest/quickest way of getting the points, so aim to maximise that.
Happy diving.
P.S. Watch out for Malcolm. Malcolm is my name for the shark swimming around who will attack you and deplete your oxygen. My headcanon is that he's the aggressive overly-protective boyfriend of the legendary gemscale nymph which appears occasionally. For me, calling him Malcolm slightly ameliorates the terror when he tries to chomp me in half. You may wish you call him something else.