IMO "appropriately sized food" for a boa is something the same thickness as the boa. You don't want it to cause a bulge (it will bulge up a bit within 24-48 hours regardless). Pythons, specifically the 'giants', can handle food that leaves an obvious bulge. While boas *can* it's generally not a good idea.
My largest girl was just over 8' and I fed her two XL rats (f/t) at one time every 6 weeks. She could handle a small rabbit, which I did a few times but at that time my source was $10/lb and it was way too expensive. The one small rabbit would last her for 2 months before she needed to be fed again and left a slight bulge. The 2 XL rats didn't leave a bulge and she did great on that diet for over 10 years. My other adults (which are in the 6-7' range) do great on one XL rat per feeding.
I am also glad you are asking questions, we were all there once trying to figure out what was best.
One of my first posts on kingsnake back in the day was 'is my boa a BCi and BCc'![]()