You'd have to use a mtb cassette + spacer (1.85mm I think?), quite a few options out there, shimano, sunrace etc. Personally, I used a cheap sunshine cassette from aliexpress ($23), weighs 500g and wears rather quickly.
Used 90s MTB/Hybrid is probably gonna be the best price/performance and shouldn't have too many issues with the weight. Also, many of them have rack & fender mounts.
Can you fit a barend shifter to the dt boss? Maybe it's also possible to get an older system in friction mode to cover the whole width of the cassette.
I found HS33 to perform better than older MTB cantis (don't have much experience with newer ones, sorry) even after 10+ years of not bleeding them or anything. Will measure clearance tonight.
You'd have to use a mtb cassette + spacer (1.85mm I think?), quite a few options out there, shimano, sunrace etc. Personally, I used a cheap sunshine cassette from aliexpress ($23), weighs 500g and wears rather quickly.