I,ve been having the same problem, this year and last. This year I took action.
I had been wondering if the thermostat was getting a bit old, and not opening or closing as it should. So I changed it today. I don't know if its worked yet but I'll find out tomorrow when It starts from proper cold.
My drive to work is 10 miles with 70% of it at 60mph. Mine usually hits 90 just as I arrive and other times doesn't go past 70. It rises slowly to 70 then takes an age to get to 90. Sometimes when normal driving it drops to 80-85.
I hope the new one makes a difference but I don't have high hopes, I've heard to golf just takes a while to warm up. But maybe they've all got knackered thermostats