Welcome to permies Frank! I think you might want to check out some of these videos by Paul of rocket mass heaters along with his
article and
Ernie and Erica's website:
I think the main solution to not having to feed it all the time is to have a high thermal mass for the insulating material- like cob or stone. Regarding thermal mass, I think these two articles
here and
here do a good job explaining how thermal mass works.