The length matters. I think there's no wrong time to invest in a good pair of boots, they're going to come in hand in a lot of different occasions and seasons. Boots are allowed in spring and summer too, you only have to wear them with the right outfit.

In this picture are portrayed a classic pair of knee-high black leather boots, with a stiletto heel: an elegant and easy-to-match accessory. 

This is how the look inspired me in terms of shopping. Recreate it on any budget here: