Yes, it's a bit of an issue at this time of year, the mats in particular.
For he mats I keep them clean with a hand held vacuum cleaner between proper hoovering. When they get muddy, or a couple of times a year, I take them out and use a foam shampoo on them which has worked quite well.
Autoglym's Fastglass is not only excellent for windows but also for any plastic trim - maybe use a rougher cloth on grained surfaces.
Most leather cleaners work reasonably well on the seats though I've noticed mine has dulled to a slightly aged look. Connolly hide cream, available from any tack shop has long been used to feed and protect leather.
After four year though I did order some new mats from the stealer, which weren't too dear. Actually, didn't cost me anything as they first forgot to order them, then got me some black ones, and never got back to me re the beige ones. In the meantime I had a full valet done locally (£70) and they're as good as new so I didn't bother.
It may be worth having it valeted and then something like Diamondbrite applied (all-in £130 at indy valet co) or you could try something like Scotchgard like you use on shoes, suede, coats etc