DHP Bulb for adult cornsnake

Hi, I live in the UK and I’ve been struggling with creating a heat gradient in my wooden 4x2x2 Vivarium. I currently have a ceramic heat lamp set up on the warm side of the Viv but after some research I believe the ceramic heat lamps tend to just heat the surrounding air. My cool side sits at like 23 degrees and my warm side sits at 25. And the basking spot sits at 29-30. I decided to add a heat mat underneath the hide I have under my lamp and it now sits at 30-32 but the warm side hasn’t got any hotter!!! It’s becoming increasingly frustrating.
I added a fan onto the warm side vent a while ago because I was struggling a little with fungus gnats and humidity but this is now solved. The fan is automatic to stop once the humidity goes to 55% and it hasn’t made much difference to the temperature at all.
Can someone give me some advice on how to bring the temperature up on my warm side?
I’ve looked into a DHP lamp but I want to double check if there’s any better advice.