2nd post – gearing support

I posted a wee while back regarding my puny leg strength and struggling on the inclines when loaded.

I'm aiming to do lands end to John O Goats this year for charity and failure isn't an option.

I took some advice from you guys and switched out the chairing from a 42t to a 38t.
This really did help however Dartmoor (my local training ground) is very very hilly and unlike other places in the UK the road planners decided to go up and over everything as opposed to weaving a d contouring. Long story short, I still struggled with a loaded bike.

I've since been picking you 2nd hand purchases with the intention of making a mullet system. (Potentially using the ratio 1×11 -1×12 mod)

Thus far I have an sram 12 speed derailleur and an XX1 12 speed cassette.

Now this is where I don't want to get caught up, I'm currently running Fulcrum 800DB wheels,Sram PG1130 11-42 cassette. I assume these are from factory as I bought the bike 2nd hand.

I believe I need an XDR free hub for my new big boy cassette but I'm unsure which one I need . Google is giving me a few options. Maybe RO202 or R0126

Please can somebody more learned than I help me out before I order the wrong thing.

TLDR: Which freehub to fit Fulcrum wheels etc for XX1 cassette?