@Sasha I'm assuming you've checked to confirm it is actually the topper thats causing the issue? ie that it doesnt happen when you're on a different sleep surface? If so i recommend wool topper from the Woolroom. Wait till they have a sale on, they have them every few wks. (edit, the one Andy mentioned looks good too, it looks thicker than mine)
I ask if you've checked because I've recently had the same problem that isnt related to the topper because i been using the same topper for yrs.
I have been having night sweats for 20yrs - waking up in early hrs drenched in sweat bedclothes wet. During that time i tried all kinds of different bedding/toppers etc & the only one that rectified it was a wool topper & thin (4.5 tog) feather duvet & cotton nightshirt. (in summer just an empty duvet cover (so a kind of double sheet).
In winter I would get the room really warm before sleep with a little electric radiator, & then as the room cooled during the night it counteracted my body heat rising. So i highly recommend wool topper - i still had the odd night sweat but not as intense, & other than that would stay same temp most of the night. Wool bedding is good because it's breathable.
But then about 2 months ago, (with no change to the bedding arrangements) i started having problems. I am now waking every 30-90 mins, too hot, even with no nightie & a ONE tog! wool duvet - so in theory a summer weight duvet in quite cool weather - its not a night sweat - i'm not drenched - just too hot, so hot i feel nauseated, like my upper torso is radiating heat while arms & legs are chilly. And then when i've been awake 5 mins i become chilly, & if i drop back off to sleep i wake up very cold, shivering. It repeats itself through the night.
Its driving me bananas. I have tried every possible permutation of night clothes, bedclothes, topper/no topper etc, it's either too cold to get to sleep in the first place or i wake up after a short while very hot, push the bedclothes down & then wake half hour later really cold. It's more akin to having a fever. I cant understand it or seem to find a way to solve it. I'm assuming it must be hormonal with me being 'that age' but as i said i was having night sweats for 20yrs & they have completely stopped to be replaced by this
keep waking up in the night too hot, throwing quilts off, and then waking up too cold later, and on and on.
So just make sure it is the topper before you shell out for another.