[oldman]

You'll probably want to just start with a startard 20"x10" seed starting heat mat that you can find in any garden center - - even WalMart's this time of year. 20x20 aand larger are available too. Get clear plastic domes for the trays you'll be using with the heat mat too.

These are basically a power cord, some low power heat - maybe 12W, and plastic to keep the heating element flat and waterproof. The last quite a while, but if you fold them, roll them too tightly to store them or set something really heavy on them you can damage the heating element resulting in only part of the mat heating up or none of it working. Damaged mats aren't usually a fire hazard or anything similar, but you should get rid of them because they are less safe than a functional mat and, most importantly, they're broken and you can't fix them.

When you buy a new one, do it locally and check that it's fully functional as soon as you can after purchase. Lay it out on a flat surface, follow any directions printed on it, and plug it in. It should get warm, but not hot. 90F range. You can write "it works" all over a couple pieces of notebook paper in lemon juice and put those on the map to test if you want to recapture a moment from childhood. It won't heat clear to the edge right away, but if there are big cold spots that persist you need to return it.

If you need more than two heat mats I'd recommend upgrading to a 48x20 just for power cord management.

Tomatoes will germinate without a heat mat most of the time, it just takes a little longer. Peppers need the extra heat, and for most of us need to be started early to give them enough growing time to fruit. But growing you own plants from seed can be as much fun as gardening outdoors.

You may eventually want to move up to thermostatic controlled heat or something fancier, but the important thing is to know what the seed you're growing needs and give them the best version of that you can. What the seed needs for optimal growth is more specific than what it needs to get started. Your real goal is plants to plant out. Thermostats and hydroponics and whatnot are overkill for one flat. But a little warmth is a good thing.