To add, the moment you enter Heavensward content, quests start to hand out high quality gear at a rapid pace. You shouldn't need to purchase gear at all unless you choose to change jobs during that part of MSQ.

As Lineage has said, just about everything post level 50 gives out Poetics tomestones, and you can purchase great gear that can last as long as level 54 with them at Mor Dhona.