Drehleierwiki has a very comprehensive list of #gurdy string suggestions, and is excellent reference if you’re not sure where to get strings, what to get, or simply want to try something new.
I’m currently using a Thomastik Infeld Dominant Viola a1 medium, (synth core, aluminium wound) as my g, some unbranded roundwound violin G (turns out roundwound doesn’t sit nicely with my gurdy) and a Violin D for the D. Planning on replacing the D with another low G set up for harmony playing, and maybe trying some gut strings for my trompettes after I’ve made new chiens.