Hi pnwtoc,
Take a look at the Perfectly Snug Smart Topper. I have written about this topper, it is pricey but works great.
A non-electric solution I’d consider is an all-wool topper. A 2–3" wool topper should provide a very temperature-neutral sleep environment while still adding some cushioning without the contouring/pushback feel of latex.
If you want to take breathability/temperature regulation even further, a horsehair topper is probably one of the best fiber options for sleeping cool and neutral. They’re certainly more specialized, but the airflow and moisture management can be excellent. I have horsehair pillows and no other fiber keeps your heat neutral.
The saying, everything between your and the floor matters, could not be more true. Therefore, I’d also look beyond the topper itself. Check your mattress protector, sheets, and comforter/blanket. If any of those are primarily synthetic materials, they could be contributing significantly to the heat buildup. For sheets, I’d look at 100% linen or 100% cotton, and a wool-filled comforter can also be a good option for temperature regulation.
Since you’re only covering half of the king, I’d lean toward wool in your situation simply because it should be easier to source/use as a half-bed topper than a latex slab, while also fitting your primary goal of reducing heat rather than addressing pressure or joint pain.
Hope this helps,
Maverick