This year it is not raining at Christmas but it is getting very cold.
I'm thinking about getting heated grips. I have read something about the K75 but I have a k100, are there any original grips?
Thanks and Merry Christmas

Yes, heated grips were available for both K75 or K100.
I suppose you still can order them at BMW, but it's pretty expensive: https://www.realoem.com/bmw/enUS/showparts?id=0521-EUR-04-1988-K589-BMW-K_100_88_0521_&diagId=32_1965

There's a complete set with wiring, easy to install.
You don't need a specific handlebar, just drill a hole at the bottom to let the wire pass through .

Or you can choose aftermarket heated grips also, but they're not as well integrated, and they are often much wider.

Or you even can choose to do it by yourself by wrapping heating wire under your grips...

If the price shock causes one to not have them, my solution which has worked for 25 years is to use ceramic resistors inside the handlebars. One will need high temperature wire as one lead wire has to come back over the resistor to reach an exit hole and a grinding wheel but it saves mucho dinero. I can't recall how many ohms on the 25watt ceramic resistors I used but included an example below. Additionally, they were activated using a relay. Yes, 2 small holes will need to be drilled in the bars to get the wires out. Once it was all working fine I filled the bar end holes with silicone and have had warm hands. One setting instead of the BMWs hi/lo. It's a hack but in 1998 the setup was under US$20. My apology for not having step by step instructions but could do so on request.

This is my unimaginative solution—with spare batteries in the tank bag connected to the power port.

The Brick is in storage when winter around here gets serious because of the terrain, the dilapidated road conditions, my disinclination to spend my waning days scrubbing road salt off more machinery than necessary, and because riding in extreme winter conditions isn't fun for me—I have nothing left to prove, even if I had something worth proving to begin with. 

The gloves could be considered costly but they can be useful on other occasions, among them: when raking snow off the roof, running the snowblower, or when frigid weather misbehavior becomes worthy of spanking.

+1 on heated gloves.  I had heated grips on two of my Bricks and used them a lot in cold weather riding.  The grips will keep your palms sort of warm, but do absolutely nothing for the back of your hands or fingers. 

On the other hand(pun somewhat intended) the gloves surround your hand with warmth.  Definitely worth the extra cost.  They also can be used for more than one vehicle(bikes, autos, snow machines, not to mention working outdoors clearing snow). 

I have arthritis in my hands, and the gloves make cold weather a lot more tolerable than heated grips.

I had not considered the possibility of buying gloves instead of putting on the heated grips, but it seems like a very interesting idea.
We will have to look for good , cheap ones.

Any suggestions for gloves other than Gerbings?

Thanks for your help.

Check eBay and Amazon.