I spent a few months on a fully packed lht with rim brakes. It was excellent, I never had a problem stopping.
What is your current set up? Can it be improved? Are your brakes just cheap and nasty or are you just pushing it past its limits?
From memory I had avid speed dial levers, 7s ring a bell With xt v brakes and brake shoe inserts on mavic 717 rims. I did have a horse shoe thing to brace the back brake, can’t remember the proper name for it.
If you really want disc and you love the bike I would probably sell the bike and buy a lht disc. People want a lht with rim brakes for their simplicity for long haul rides where spare parts are hard to come by so it’s probably still worth a bit. It’s also a surly so they hold their value.
Otherwise, just go front disc as above.