If you're looking for big, extremely chill, and overtly lovely (patterns look like flowers), go with a female Dumerils Boa. They are very laid back to handle and petable. Level of food aggression is very low as well. You'd be looking at around 7 feet and some girth. They don't chow down like retics. My adult female takes a large rat every 2.5-3 weeks, and sometimes she stretches it to a month. Poop and pee load is also less than the retics and burms.
I have her in a 72x30x15 with a shelf because she likes to stretch from the floor to along the shelf and she displays well. She was in a 48x30x15 with a shelf and that also worked well. Most Dumerils don't seem to care about a shelf, but Belletrix hangs out a lot, just relaxing. Dums slow grow, which is also a plus if you have younger kids. And you can get a really nice baby for around $150-$250.