I'll list a couple I own or owned and love and will end with a tip:
- Panasonic 15mm f/1.7 - my current favourite, a great performer, compact, but probably too wide for you.
- Olympus 17mm f/1.8 - the 15mm's predecessor in my collection, pretty nice lens, just not quite as good across the frame as I'd wanted.
- Olympus 25mm f/1.8 - a small, light lens that performs very, very well; I think you'd be very happy with that one.
- Sigma 30mm f/1.4 - on the big side, but certainly not a lot bulkier than the adapted lens, very strong optically, and very versatile.
- Sigma 30mm f/2.8 - small, capable, but not the fastest in terms of maximum aperture. I loved that lens when I owned it, but it was superseded by the Olympus 25mm f/1.8 a little while later, and that lens is a better performer as well as faster ...
If you buy used, all except the 15mm f/1.7 should be available around $200. The 15mm will set you back used between $300 and $350, I'd guess. From your description, I think the Sigma 30mm f/1.4 would fit the bill best - I own that lens and find it very rewarding; it's also the only lens I ever bought in two different mounts (Sony E,
), and I've never regretted that decision, either. Other than that, the little 30mm f/2.8 is a charming lens in use - but it's a bit on the slow side for
...
However, if money's tight, the real sleeper is probably the Panasonic 25mm f/1.7 - it's the cheapest of all those I mentioned, focuses a lot faster than the 20mm f/1.7 you know and is optically pretty much as capable. It's cheaper new than even the Sigma 30mm f/1.4 used.
M.