I looked into OTR a lot when I started to work on fixing dms. It got scratched pretty quickly because, groups. Sorry to say but I think you’re the odd man out.

nostr:nprofile1qqsy2ga7trfetvd3j65m3jptqw9k39wtq2mg85xz2w542p5dhg06e5qpzdmhxue69uhk7enxvd5xz6tw9ec82c30qyvhwumn8ghj7un9d3shjtnndehhyapwwdhkx6tpdshs0j22z8 has the double ratchet stuff that he’s been working on recently that does pairwise dms. But I’m not sure if any clients have implemented it yet.