Have you looked at the aircraft spruce website. They have a number of mains powered oil sump heaters. These are stick on electrical heaters which will warm the oil. For Lycomings they stick on the sump, but I think that Yaks have a dry sump with an oil tank so the heater will need to be stuck on the oil tank. I'm sure there are websites.
Good idea to use a sump heater, it saves using all that avgas to run the engine up to temperature before takeoff.
One thing to remember is not to use the oil heater all the time. Aparently, if you do, the moisture/acids evaporate and condense elsewhere in the engine and do more damage than being left in the cold oil.
So use a remote controlled switch to turn the heater on 1 hr or so before flying.