Just preorder Lightfall and wait until then. Reason is anything else you'd buy is already pretty stale, you'll have trouble finding help on older content, when you do find it, they'll probably be more a hindrance than anything else, and you'll be in catch up mode for a long time only to get soft reset at LF anyway. Just play seasons for now and be content to be locked out on content. Maybe get the Dungeon next season. Get warmed up and little then dive in for real for real in Lightfall. You'll have a much better experience.