Self-inflating topper for 3-seater Beach?

[Blakey]

I have a couple of Vango self-inflating double mattresses (https://www.campingworld.co.uk/en/Vango-Adventure-Double-Self-Inflating-Roll-Mat/m-5815.aspx). However I'm wondering if there is something similar which more accurately fits the downstairs of my three-seater Beach.

Anyone know of one?

Thanks
Blakey