mighty hatch
So the idea would be similar to bedrock and how they have given over time, some free cosmetics. It doesn't need to be a big wave of these but like maybe every once in a while, there is some sort of cosmetic that relates to what achievement it was tied to. reason I say this was because I saw people wanted to suggest coins for achievements or something, but i think giving players some free stuff to earn or just have more defiantly would help a bit more to alleviate the feeling of not having enough cosmetics. I do think bedrocks style of giving some free cosmetics on achievement would help give some free players something while still having the shop for some extra cool cosmetics exclusive to the shop.
example could be for like the taming achievement, for that it could just give maybe a vanilla Minecraft wolf that is in the style of the classic wolf before the Tricky Trials update. Or maybe the redstone achievement giving some sort of redstone related outfit or copper engineer goggles with redstone on it? Just ideas for what kind of cosmetics they could have set if this was to be a thing. Again it doesn't need to be in waves but just maybe like a small handful of them every few updates when they can.
crude pulsar
radiant thicket
keen agate