I'm a life long Pentax user too and have a half closet full of bodies in various states of working...
My most reliable one was/is the K1000 I purchased new in 1985.
But, you said no to Pentax so in light of that, how about a trusty Nikon FE, or as Bryan mentioned an Olympus Om-something or other.
I have the Om1 and Om2n as Bryan does and they both are nice sleek little machines.
They work and perform great, but I don't like the business of changing aperture at the end of the lens. I'm just not coordinated enough to utilize that in a logical field user fashion.
Oh, and another all time favorite has been a Nikon N80.
It's a nice user and the auto focus is perfect with those of us with aging eyes...
Some are put off by the plasticky body, but I have found it to be a marvelous thing as it is lightweight and takes quite a bit of rough housing in a camera bag without much worry. It truly is an all day carry and I personally feel it is smarter than me for metering and especially focusing.
With all that, The Nikon N80 would be my first choice if I was starting fresh as a film camera user.
You can use it in manual setting too.
Nikon glass is mostly always good and with some sleuthing, you can get great glass at a reasonable price.
You can find them in good shape for under 75 USD, and when the bottom fell out of film camera prices a few years ago, they were easy to find for a twenty.
the battery is pricey, but lasts forever.
Good luck in your search.