Which heat lamp(?) is best?

[Brixxart]

So, I kinda sorta impulse bought a bp this weekend, whoops.

I had already been looking into their care so I bought all the supplies I need..

But... my 20g tank doesn't seem to be keeping heat. at all.

I have an UTH which is on a light dimmer, with a temp probe against the glass above the mat which reads 90 degrees after hours of running it to establish the stability.

But I have a hide over that area... so outside the hide is all... 72-75 degrees as is ambient in my home.

So I was looking into maybe getting a heat lamp as well? Ceramic heat emitter best? Which brand? Which dome? How to mount it? Could anyone be so kind to provide me links on amazon to which would be the best for me to buy? Thank you so much if you could. Would I need a second "thermostat" or lightdimmer?