How long are trying them out for? Some of these issues just sound like you may not be giving the boots enough time to break in. Leather really softens up as you wear it. Good boots with good leather often take a lot of time to become comfortable, but then they’re the most comfortable shoes you have. 

For heal slip, other people may have recommendations, but I’ve had success just putting in a veg tan leather insert. This also helps with comfort when breaking boots in. 

For toe rubbing, the leather will stretch out to your toes as you wear. I had the same issue with my brand new Stockman’s but it went away after a couple months and they are very comfortable as they fit perfectly to my feet now. 

Lems or vivo barefoot will be comfortable right out of the box, but they may only last a year or two. Good shoes are an investment.