If you want the mattress to be a bit softer, then this could be a good choice. No matter if it's hot or cold the mattress can compensate for that thanks to how it's built.
From Amazon
Silentnight Ultimate Deep Sleep Small Double Mattress Topper - Extra Thick Deep Luxury Mattress Enhancer Pad Protector Bed Topper Providing Ultimate Comfort - Small Double - 190 x 120cm
Wayfair
Silentnight Ultimate Deep Sleep 1000 Mattress Topper