Welcome!
I think that camera allows you to use pretty much any Pentax
K-mount lens that has an aperture ring on it (ring with little f-numbers, like f1.7, 2. 2.8, 3.2, etc. usually up to f16 or f22, sometimes with a special A setting, which is useful on newer cameras, but useless on yours unless I am mistaken). There might be some exceptions in terms of compatibility, but those lenses are rather rare anyway. I would recommend you avoid m42 and m39 and m37 mount lenses for now, as those require an adapter. So, K-mount bayonet, also called K and then its newer incarnations KA, KAF, KAF2, etc. Sometimes its even called KR, for Pentax-Ricoh. You'll figure it out as you go along, don't worry
You can go here:
Pentax Lenses - Pentax Lens Reviews & Lens Database
And scroll down to M series. These are usually fairly affordable and good quality, especially the primes (fixed focal length - zoom lenses used to be rather poor and only recently have become great, but at a hefty price tag). As you can see, there are
a lot of lenses to choose from. Pentax K-mount lenses have been in production for decades, by various manufacturers.
In your case I would recommend maybe a Pentax 28mm or 35mm lens for general wide angle (landscapes, street, travel), and a lens between 77mm and 135mm for portraiture. The smaller the mm number, the wider the angle of view. The lower the f-number, the more light the lens can capture. The M 50mm f1.7 is a good place to start, though.
The good thing about Pentax K-mount lenses is that you can even use them on modern digital cameras, like the top notch K-1 or the affordable K-S1. Of course, if the lens pre-dates AF or other features, it will not suddenly develop those once you put it on a new camera
One more thing - maybe you will get more answers to your question if you post in the film SLR subforum. It is also possible someone already had a similar question to yours and it got answered there. In the US I think there is well-respected guy named Eric that does a lot of this kind of stuff, repairs and refurbishing and general CLA. I'm sure his contacts will pop up in relevant threads, so just go search those forums