I don't do anything for mine by about 4 weeks old, and they do just fine. The first nights they pile up in a puddle of feathers and beaks to stay warm and for security. I never use a heat lamp. Not ever. I'm just like you - I don't trust them, I don't like the risk of fire, and I believe they keep chicks from experiencing the natural day/night cycles that they'll have to get used to when they do go out. Chicks under a heat lamp just never get enough sleep. Even if one poor little fella dozes off, it's only until another more wide awake chick stomps on him on the way to the feeder or water.
I brood my chicks outside, in a pen within the run. The Bigs and older chicks can see them and they can see and learn from the older birds. By 4-5 weeks they are out of the brooder pen and fully integrated with the entire flock. All I use is a heating pad draped over a metal frame, a towel, and some straw. When the sun goes down they settle in for the night and sleep all night long, raring to go in the morning. They thrive. Oh, and our temps when these babies were outside in the run? A balmy 17 to 23 degrees. It snowed one night when the second batch of chicks was only a few days old. In fact, it snowed sideways with wind gusts of 60 mph. We even lost power out there and didn't realize it until we woke up to the sound of power coming back on. No problems. This system is now being used by a whole lot of people who are having the same results. Here's the thread, if you'd like to see some of the videos.
https://www.backyardchickens.com/t/956958/mama-heating-pad-in-the-brooder-picture-heavy-update
Anyway, I digress. By now and with the comparatively warm nighttime temps you have in your area, your chicks should be absolutely fine be in the crate without that blanket. A blanket works for providing warmth by trapping body heat, and if it's nowhere near their bodies it's not really doing anything except holding in moisture from their breathing, their droppings, and their water and blocking drafts, which they shouldn't have blowing on them anyway. You should be perfectly safe just letting them learn their new surroundings from the safety of their crate until you are comfortable integrating them. These little critters are a lot tougher than we give them credit for, as is evidenced by watching a broody take her little flock out in 20 degree temps and letting them explore. They just dash under her if they get spooked or for a quick warmup, then they're out running all over the place again.
