Alternative mattress which has heat reflecting properties

About three years ago we purchased an Artisan 1500 medium after quite an exchange of correspondence to get it right. We liked your website and customer service which is why I’m writing to say we didn’t get it right. After a couple of weeks I wrote to say in retrospect we should have gone for something harder as the mattress seemed lumpy and you kindly offered an exchange. After all my research and the upheaval of delivery I didn’t take you up on the offer hoping I’d get used to it. It has a cashmere layer and it seems to reflect the heat so we are hot all year round , far too hot in the summer and I’ve never liked the tufts which can be felt through the cotton mattress protector and bottom sheet.
Have you any suggestions. Do you make anything cool to go on a slatted bed base preferably with a flat
Surface that doesn’t have lumps. I’m 9 stone and lie on my side and my husband is 15 stone and sleeps on his back.