See if you can get hold of a Pentax-M 135mm f3.5 to extend your range a bit, they're tiny, light and sharp and as it was a standard telephoto they're plentiful on ebay. You can find minty ones for not a lot of money so don't pounce on the first you see, I have a near perfect one here which cost me about the same as three rolls of decent film.

The Pentax-M 100mm f2.8 and 120mm f2.8 are very lovely but rather harder to find (therefore much more expensive). I have the earlier K 120/2.8 which I would never sell, it just feels spot on with my K2.