Car seat protector for ERF seats?

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We moved our Axkid minikid from our old Focus to our new S max this morning and it has left big dents in the car seat foam (at the front of the seat under where a passengers knees would be). Not a big deal this time but I would like to prevent it happening in the newer car if possible.
I think because it's ERF so the heaviest weight (back of the minikid) is on the front edge of the seat, and the way the minikid tether straps in particular ratchet down it really does push the minikid quite far into the foam unlike a FF seat would. I see car seat protector mats on Amazon but they don't look particularly solid, more made for FF or to avoid scuffs to leather.
Equally I don't want to prevent the seat being fitted properly so I don't want anything too slippery (I'm confident I could still get it rock solid though, it's such a good seat). Some kind of fairly hard rubbery mat thing would be best but I can't find anything like this.
Anyone else had this issue and managed to solve it?

Can you cut a square of plywood for the seat to sit on, that way the weight is spread evenly.

Thanks; good suggestion although I can't help but think that would cause even more damage to the seats! Maybe something a little less hard/potentially splintery.

The foam should pop back out into shape, I don't think it's safe to put anything underneath, but if you ask axkid they'll tell you for sure.

incarsafetycentre.co.uk/product/ultra-mat/

I have this under the same car seat

We have the Venture car seat protector, which Amazon sell. I can't get it to post a link I'm afraid.

Interested to see the recommendations here, we have the same seat and have been looking at car seat protectors. DS is nearly 3 and generally climbs in on his own now, but that's starting to mean muddy footprints on the edge of the seat. The Diono one doesn't look to be quite wide enough to cover the edge of the seat and prevent that but it's the only one I've seen that's been crash tested

Thanks for the suggestions. I don't think we can count on the foam popping back into shape, the seat won't really get moved at all. It was in the same place in the old car for 18m.

Hi the way to avoid this is to remove the seat every month or so and allow foam to spring back. Then reinstall.

Please don't use plywood or anything. It will affect install and become a projectile.

Also you could alternate seat position.

The Diono Ultra Mat is very thick, I have various ERF seats and using that protector means the marks they leave on the seat aren’t very deep at all.

www.preciouslittleone.com/product-information/41/27587/diono-ultra-mat-(black)/

Just read all the comments properly, the Diono May I have is plenty wide/deep enough to cover the whole seat, in fact I have to fold a corner of it to get the seatbelt buckled in. My car is a Peugeot 5008, sonit has three individual equal-width seats like the S-Max and the buckles are recesses down into the seats.

^ Diono mat I have!

Thanks all I have bought the Diono though am saving my energy til the weekend to undo the seat and put it underneath :-)
One pain with the s max is DD can't climb up into the seat herself like she had started doing in the focus, she's very annoyed! Also the bit where I bump her head almost every time i put her in is bare metal in the s max not covered in rubber, which I discovered this morning, sorry DD!