I tried a 'boiler-style' 2-gallon humidifier the first year I heated with coal, as it worked sort-of OK with my natural gas forced air furnace. Then I decided I needed something better, and cost-free to operate.
So, I started hosing down the painted concrete basement floor where my stove is, and put a cheapo box fan blowing the air essentially 'in a circle' around the basement (center of house stairway). It was OK, but I still wanted more humidity. So I started hanging 5-6 soaking wet, large bath towel sized rags on a line in the basement. I did this twice a day. OK, but after 2 years, I got tired of filling the basement wash tub, dunking in the rags, etc. So this year, I've changed my schedule to 3 times a day, but hosing the floor only. I stay a lot drier as a result.
Note that I also have a floor squeegee, and that I only hose down the area directly accesible from the sink, which covers 2 sides of the house and the one side up to stairwell. There's a low spot in the floor about 8 feet in front of and to the right of the stove. So after dumping the ash, filling the hopper, and cleaning the glass, I squeegee any standing water into the hard to reach areas, then spray with the hose. Additionally, I have the basement door removed, so the warmed air in the basement naturally drifts upstairs. According to my digital temperature/humidity meter in the living room, the humidity stays somewhere near 44-50%. So I can't complain at all. Living alone does have it's benefits.
One more thing...it took me 3 seasons to finally 'perfect' my air distribution system. I simply 'plugged into' the main hot air trunk about 4 feet from the furnace, and experimented with how to get the cold air back to the stove. I tried fans blowing down the basement steps, tapping into front-of-house cold air returns, and finally settled into tapping directly into the main 'down plenum' cold air return just before it goes into the furnace. That seems to work best. Note that I have a removeable 'blocking sheetmetal' preventing backflow into the furnace hot plenum from the stove and I'm using 2 inline 405 CFM fans to move the heated air around the house.