...did someone mention being interested in boas? Because I thought I heard someone say they were interested in boas.
OP: If you're looking for a manageably large, relatively easy-to-care-for pet snake with a mellow personality, a Columbian BI (Boa imperator) boa is probably your best bet. Your average male will probably sit around 5-7 feet fully grown, and your average female will be 6-8 feet. They're pretty hefty and muscular for their size, so a full-grown one is an impressive animal, even if it isn't a giant! Columbian boas are often described as good "shoulder pets" within the boa community, as they're typically well-natured and not excessively grippy (like BC [Boa constrictor] boas), flighty (like some locality boas), or sassy (again, some locality boas). While many Columbian boas will reach the size where it's a good idea to have a second person in the room just in case (such "size" is typically quoted to be between 6-8 feet), you're much less likely to run into trouble and need that help with a boa than your would with other species.
For reference, the boa Gio posted a picture of is a very nice Barranquilla, Columbia boa by the name of Sniper. My first snake was almost a Barranquilla boa because of him.
If you're looking for more boa books, I'll put in another recommendation for The More Complete Boa Constrictor by Vin Russo and a new one for The Boa Constrictor Manual by Philippe de Vosjoli, Roger Klingenberg DVM, and Jeff Ronne.
Good luck! And good on you for doing your research now instead of rushing in and asking questions later.