Take your oxygen hose into the shower with you. Wash top & sit and rest, wash bottom & sit and rest. You just have to slow down (easier said than done --I know ) It sometimes takes me 30 to 40 minutes to shower. I have found that it's easier to shower first thing after I wake up.

Thinking about getting a shower seat to help.

I cant add anything to help . But your not alone Im exactly the same & from Scotland Kilmarnock. Chin up 💖

I just toss my cannula over the shower door when I shower. I also have a shower chair that is a big help when I get out of breath.
Going up hills or stairs is a big no-no for me at my level of COPD.
I have extremely bad back pain when I get out of breath. It eases up some when I get my oxygen level back up.

You can shower with your oxygen on.