Welcome, and well done. That's a very nice camera to start film with - easy to load, easy to use, aperture priority for any lens you can fit, and P mode is there for you when you need or want it (and the lens allows). I have one, and if it lasts it will be my children's training camera.
Your choices below 50mm are mostly 28mm (minimum zoom for your lens) or 35mm, but there is the SMC-M 40mm "pancake", which makes your camera exceptionally small and pretty near pocketable (depending on the size of your pockets). However, it may not be wide-angle enough for you.
Before buying any glass, I would take a couple of rolls with the lens you've got, getting used to it and getting a feel for where the zoom ring ended up being set when you took the shot. You are sort of blessed in having bought yours with a zoom lens, in that resp[ect. The most common result you get is the focal length of prime lens you should then start to look for. If you wind up being zoomed in a little, you might look for a 35; if you are taking a lot of shots zoomed all the way out, it needs to be a 28mm.
That being said, there is a lot to be said for having a fast fifty, even a relatively humble f/2.0 kit lens; they are plentiful, therefore cheap, and they offer creative aspects in terms of isolating the subject as well as enabling hand-holding at much lower light levels (remember, you can't just turn up the ISO the way you can on a digital camera). The Pentax-A 50mm f/1.7 has a wonderful optical reputation and will work hand-in-glove with your camera, but the aperture ring is plastic and has a particular failure mode after all these years, so if you go down that road be sure to buy a good one you can handle, or from a buyer who accepts returns.
The Pentax-M variant of that lens is just as good and tends to be more mechanically sound, but won't offer you full program mode, only aperture priority. This may or may not be an issue for you.
Something else I would consider, if you don't already have one, is a sturdy tripod. It need not break the bank; it just needs to not wobble if you so much as touch the camera when it's mounted thereon (try it out with the zoom lens attached and zoomed all the way out). If yours is one of the models that has a threaded point for a cable release (some do, some don't), you might consider getting one of those too. However, the P30T does have a self-timer, so that's less of a priority.
And finally, of course, if you end up going Pentax Digital at some stage,
all your manual glass will work on Pentax DSLRs.
(The reverse is not true; Pentax DA lenses have no aperture ring and will default to full program mode, and both the wider primes and the zooms will not cover the whole of the film with their image. But cross that bridge when and if you ever come to it.)