Happy New Year and a successful tomato growing season!
Santa brought me a large electric propagator and an LED grow light to replace my old set-up, so I have the chance now to sow tomato seeds even earlier than usual.
One of the problems with sowing early is that plants can become too leggy - especially if there is not enough light. Therefore, keeping seedlings at a mild temperature requires some artificial lighting in the form of a grow lamp/light.
Getting the combination of light, heat and moisture correct can be tricky because too much heat and moisture and they'll shoot up like rockets ... a temperature that is too cold will slow or even check growth and plants may not recover.
Keeping a minimum of moisture in the soil (under-watering) is my approach when conditions are cold. When temperatures are warm and light levels are high, tomato plants are happy with plenty of moisture, especially when they are fruiting.