I use the top of the water heater tank! Some people use the top of their refrigerator.

I grow cuttings and seeds in my basement where the temperature is much like yours. This year I bought a large heat mat and the difference is amazing. I use it for germination but I leave the heat mat on after they have sprouted. I use a mesh tray with a couple of pieces of 1x2 along the edges. Then i place my tray in that. This raises the tray about an inch but leaves the heat surrounding the plants. I bought a small magnetic thermometer and put it on my light fins. It shows the temperature has risen 4 degrees. Even my large heat mat only uses the electricity of an incandescent light bulb. Much cheaper than running a heater

We installed a shelf on the wall over the pellet stove. Check them 2x a day, anything that has sprouted gets pulled and put under grow lights in dining room. Works extremely well.

I float plastic trays in water with a fish tank heater submerged in it. Advantage 1: you can dial in any reasonable temperature within a degree or two. Advantage 2: tanks are BUILT for lights!

I also grow flowers from seed in a basement, though it's furnished so it's generally not too cold. I used to use heating pads (like you use for relaxing muscles), but it actually heated the seedlings too much. Now I just allow them to gain heat from the lights underneath, which are strapped to the wire frame of the shelves with velcro. If they need a heated environment to germinate, I put a plastic top on them, then take it off when they've sprouted.