Click on pictures for larger picture.....

I like a heated long sleeved shirts or maybe a heated fleese long sleeved zippered something.  There are all sorts of possibilities.  Currently, I'm using this one that I'll supply pictures of.

Most of the time a commercial heated jacket go on the outside of all your other clothes, and they draw about 10 amps and require a heat controller (about 80 buck) to keep them from being too hot.

My shirt will draw about 5 amps and give you all the heat you want, and can be used closer to your skin which is why it doesn't need so many amps....like a commercial heat jacket uses.

So the numbers that I developed are 55 ft of 26 gauge insulated stranded wire.  The 55 ft keep, and no less, keep it from being too hot, but requires that you stringing 55 ft into your shirt or whatever you use.   I take a small soldering iron and make holes in in the fleese or whatever.  The material must melt.

55 ft are a lot of feet.  I can run 4 rows of wire in the front of the arms and about 26 other 18" long runs up and down the front and the back of the jacket.

Oh, here's another material that already has the holes.  I use this also.  I'm sure you've seen shirts made of this stuff.  It's usually a sports tee or sports jersey.  This one shows safety pins that pin it into my jacket for the winter season.  It also shows the kind of electrical connector.  Since this picture was taken, I now glue that joint to the shirt by smothering it with a couple inches square of clear silicone sealer.

 I use a 2 terminal flatwire connector called an SAE trailer type connector.  You can get them at Napa or Autozone, or....and I run the wires like in this picture...there's a front and back view.

A bigger picture (copy and paste)...  https://photos.app.goo.gl/MZQ5KCtxY6I83AZh2

Running 55 ft of wire takes a long time so I run a 26'or the right and 29' piece on the left and do each wire backwards and meet them in the middle in the back and join them there with a solder and shrink tube joint....then I smother that joint in silicone sealer and glue it to the shirt there so it can't be pulled apart.  Picture attached of the back joint and the 2 wire connector that attaches in the front left of the jacket to the bike's power supply.  Smother front joint as well.

I use my zippered fleece jacket as either a stand alone jacket and zip it up, then put a jacket over it.  But sometimes I safety pin it into my jacket with about 20 S pins and leave it in my jacket all winter, then unpin it when the weather warms up.

If I use one of the sports tees with the holey fabric, I cut that down the front and safety pin that in a jacket for the winter.

or I don't cut it , and use it as an electric tee shirt and put the t-shirt on and leave it on all ride, if it doesn't get too hot.  

I regulate the heat by putting layer shirts underneath to insulate the heat from me....or take a layer off for more heat.  A heat controller is a big help but it's expensive.  An on/off switch on the bike that is easily accessible is a big help so you can shut the heat off and turn it back on depending on how hot you are. 

Once you get on to making these things, you may build too many of them, and not know which one to use...when.

If you smother the wire connectors with enough silicone so the wires aren't open to water, then washing is no problem.  I don't dryer mine.  I just let them dry. 

When I hook up pants I have two 2 wire connectors at the lower front left.  I hook the pants to the shirt and the other shirt connector to the bike's electric system.

Now you are using 10 amps of juice.  That's quite a bit. Most bikes have enough for that but you might be getting to the limit of extra juice that the bike has.    I have done it, but find its rarely that cold once your upper body is warm.  It's less complicated to just wear some outer pants that are wind proof.

Also in my wiring picture, there are 33 vertical wires in a short sleeve version and 26 wires in a long sleeve version because a bunch of wire goes in the arms.

Chaps or rain gear make a great wind stop. 

Plain insulated wire works fine (it's not silicone).  I have used teflon coat wire, but it slippery and wants to bunch up and has to be straightened out from time to time.  If I make another, I won't use teflon.

Cotton is no good as it unravels when you make holes.  It needs to be polyester because it melts for the hole and seals all the loose ends.

You ask about the perfect temperature.  These things are never a perfect temp.  It will be hot enough for the coldest conditions....and too hot for riding in 50 degrees.

You need to be able to turn the heat down.  I do it by placing my heat garment at the right place in my clothing.  I live in SD Calif. and don't deal with too cold of conditions.  So pinned into my jacket and on top of my shirts is great for me. 

 If I got into colder country, I'll use my heated tee shirt and then put it on top of my undershirt.  I get much more heat to my body that way.  If it gets to hot, I turn it off with my switch.  

Cycleing from cold to too hot to too cold again can take 20 minutes or so, so turning it on and off isn't a nuisance.

Here's a cold weather ride... http://wfifancold.blogspot.com