Hi, what is the scale length? is the guitar electric or acoustic? is it set up for fingering or slide? I'm sure that info would help.
https://www.cigarboxguitar.com/seasick-steves-3-string-doghouse-tuning This might help you find what you are searching for.
I have to laugh that Shane starts this vidoe with the verboten fly-by's he now says not to do, lol
it's an Open G3 chord tuning
8vb (ottava bassa),1,3
Flat Wound strings are best for fretless and slide because they produce that unwanted string noise, but they cost more. They aren't as bright sounding though as the round wound strings.