You would want one that is made from natural material , ideally organic, in order to better 'connect' to the earth through asana. I find cotton to be the best and its relatively cheap. The ancients who founded yogasana didnt use mats and practiced outside on the earth and thus they were very grounded and connected.
I would advise against a plastic one as it acts as a barrier between earth and you and wont ground you as well. You could also try a natural rubber on.
I like the look of this one :https://ishashoppe.co.uk/products/isha-cotton-yoga-mat?variant=14994539910 its £29