Most modern coolers will provide sufficient pressure to spread a pea sized amount of thermal paste to cover the whole cooler.
There are also thermal pads, both reusable and single use, that perfom well and don't require any guesswork.
If you want to paste, noctua has the best paste in terms of thermal resistance, but mx4 or mx5 both perform well, as does cryorig and a bunch of others.

Maybe next time I have to explain to my designer why the email is so much work to craft maybe I’ll send them this article instead.