There are so many Pentax lenses to choose from in that range. Like you, I have the K-1, and I also have the D-FA* 50/1.4. For sure it can take the very best quality photographs, a pixel peeper's delight, but now that I am in retirement age and less fit than I ought to be, I find lugging the D-FA* 50/1.4 around for more than a couple of hours a bit of a chore - unless it is in a back pack with a couple of other lenses. My walk about lens is the D-FA 28-105, but if you are looking for a standard prime consider the following:
The FA 50/1.7 is, in many respects, better than the FA 50/1.4 which is probably more of a portrait lens, (it also takes me back to my first Pentax MX with M50/1.7!)
The DA 40/2.8 Limited is so miniscule you might not think it's there, reminds me of the 1.7's sibling the M 40/2.8.
I do agree with comments about the FA 43/1.9 Limited, it's a little cracker!
Macro's tend to focus hunt when I don't want them to so I keep them for their intended purpose,
But the unsung beauty is the DA* 55/1.4 It's a softly spoken SDM rather than a whiney screw focus lens, and it does take sublime photos. On full frame you will only notice the slight vignetting when it's wide open, and can easily remove it in post processing.
There are some lovely photos taken with it on the K-1
here and some test photos
here.
There are others, but maybe we already have too much choice with the above.