At one time I only bought feather & down duvets but got rid of mine when I developed an allergy. I now know that feather & down had nothing to do with it, but the deed was done. As a replacement I bought a Fogarty Soft Touch duvet from Dunelm and it's great. In fact, I've got two on my bed, a KS 7.5 tog and a DB 4.5 tog which acts as an eiderdown in winter.
It's a relief to know it's not just me that gets warm. By the middle of the night I'm like toast. When I had a series of acupuncture in 2016 the chap told me I had an overheating problem but he was concentrating on the arthritis so he didn't deal with that. I didn't like the needles in my feet so I didn't book a second course.
I use have the problem of being too hot in bed, but the last few years I have felt the cold more. The 4.5 is perfect for spring and autumn I find. If we get really hot weather in the summer I have a fan in the bedroom or sleep under just the duvet cover.
I often wonder who sleeps under these 13.5 togs, especially if they are married. The shops seem to mostly stock these.