Heat mat for mature plants?

As you can see, my current chilli pepper plants have outgrown their current shelf. I am setting up a different space for them in another room. They will have more vertical space and three Barrina T8 lights.

So far they've grown on a heat mat because otherwise they're in our coldest room. The new set up will be in a smaller upstairs room that tends to be hotter, 24 or 25°C when the house thermostat is set to 21. Should I add a heat mat still, or leave it out in their new environment? Add it but turn it off during summer, when I'm sure the room will be even hotter?

I'd love any general advice on this topic. This is my first time growing chillies! Last year my bf bought some novelty 'grow your own chillies' kit and tried to grow them in pots outdoors, but we're in the UK and they were clearly struggling due to the weather. In autumn I took over, brought them inside, and basically babied them all throughout the winter. It's really exciting to see them starting to produce peppers, and I wanna do the best possible for them!