What you wear at any given tempature will be different than what I will wear, so there are no hard and fast rules.
But I will suggest that you look into knickers. Not shorts, or full tights, but come to just below the knee. I find they are perfect for chilly mornings when tights would be too much, and short not enough. And they keep the knees a bit warmer, which for me is important. I will tend to put on extra layers on my torso, vest jacket, etc. with the knickers, and have the option of taking that off if\when it warms up. The knickers are good in a wide range of temps.
YMMV