legendary backpack
Do you plan on switching stats constantly? Getting the ascended backpack from ember bay would actually be the shortest path.
If you didn’t get the PvP backpack started by now, it’s too late to get it this season. Since we don’t know how hard it will be to get it after this year ends, it’s a risk to start it now. So that leaves you with Ad Infinitum, which is heavily time gated by fractal research pages (about 3 months for 3 sets of 28 pages if you’re unlucky!), and is going to cost you thousands of gold. But it’s more viable than the PvP one if you didn’t start that yet.