TBH, I think if you have leather seats then you already have good wet weather covers! OK those leather 'covers' will need a little routine attention. A regular wipe down with wool detergent in warm water will see them clean. Or if you prefer, Lexus do a good leather care kit that really cleans and protects the leather.
A you say, the towelling covers are great for hot weather and protecting against sun cream and moisturiser. My good lady seems to bathe in the stuff ....