I hope its not too late to reply, my OH and I both have a fleece cover. I got one because I thought it might add softness and keep me cool in the summer and warm in the winter. However the seat I had at the time, the shape of it, meant that the cover meant I was slipping around for some reason.
Later I changed my seat to a much more comfortable one but found that the 'non slip' material it was made from gave me the opposite problem, my trousers rode up because the fabric clung to them and also Im a very nervous rider and cant 'step off' the bike when I stop which means I have to slide off the seat, because of the non slip, it meant I sort of 'dragged' on the seat and it made me even more nervous, so I decided to get another cover for me (my OH had nicked the first one) and so I have one now
The first one I got from bikester and the second one which is pinky/purple/marsala which matches my bike perfectly was from griege
They dont make the seat any softer by the way