Had exactly the same thing on mine a few weeks back. Barely ever got up to 90, only if you idled for bit after a run. Generally sat at 75ish or less whilst driving.
Bought a Gates stat for £5. Took a couple of hours to fit, I found it impossible without moving the alternator to one side, even with all the tools I have! And the alternator although easy to remove, I found a pain in the !?,@* to get back in position again.
And like 747-727 said, get a new dipstick tube... Even after reading about all the dipstick breakages, and being as careful as possible... It still snapped on me lol
Temp is perfect now, warms up quicker & doesn't budge from 90°c no matter how it's driven.
Good luck.