The Spotmatic F, ES, and ESII were the last and latest screw-mount Pentax models produced, and these are the only three that offer open-aperture metering, and then only with SMC lenses. The ES and ESII have AE, and no user-selectable speeds below the 1/60 X-sync speed.
For ALL the goodies including mirror lockup, shift focus to the K-mount and look at the K2 and K2DMD, or the later LX. Even the tiny MX has interchangeable screens, using the same ones as the LX. Using M42 lenses on these loses diaphragm automation though, as with (AFAIK) all other adaptations to non-Pentax mount bodies too.
From what you've said, I agree with those who suggest the Spotmatic F as a fine choice. While I have 15 Pentaxes, the F is not among 'em.. 🙁