nothing you can do about sagging as wear and tear, you can buy replacement foam bolsters from capital seating, i did, pain of a job but worthwile
as for cleaning youll get mixed answers to what products people use, i tried several and been to valeters of the years but was never happy so went out and bought vax carpet washing machine and used that now once or twice a year and just use autoglym uphol cleaner in between the marks you get on bolsters, lot of people use suedecleaner on bolsters which works well