Icy veins has a good guide on upgrades, but the TL;DR is that adventure gear only needs Flightstones for the first half, and then Whelpling crests for the second half.
Adventure gear is rewarded from world quests and such. You can get up to Champion gear without stepping into a raid or M+, but its generally only acquired from certain group events out in the world like Fryakk assaults.
I haven’t tried AQ yet but Un’goro advanced is ROUGH. The best I’ve done so far is 2 seconds late for gold…