Do not buy the thin twin breakers until you check the local code. In RI, they are NOT allowed. It does put unnecessary stress on the spot in the panel. I am amazed at some of the things people do with their panel and running new circuits. Anyone ever hear of electrical fire?
Two weeks after we moved into our present home in 1994, we had an electrical fire. Had I not been in the basement at the time and a fire extinguisher close by, I would have lost the house. Flames were shooting out of the panel! The entire panel was toast and the wire burned on the outside of the house, all the way to the connection from pole to house. The cause was a secondary panel the original home owner added to the main panel. The wires were very loose and we all know a loose wire causes resistance which produces heat. We were very lucky. I had to spring for a new service which I had upgraded to 200 amps from 100 amps. We couldn’t live in the house for a month until it was cleaned up from the smoke damage and new service installed. My insurance company had a 40 foot trailer delivered to our driveway which we lived in while the repairs were made. Oh, my insurance premium almost doubled after that fiasco.