I would say go with a blue tongue skink like you had planned. A male Merauke will grow close to 24" like my Homer. A 4x2 glass tank is best, they are smart and like to watch the world outside its tank, and the feeding is easy and fun (omnivores with a love for canned snails) about once or 2x a week as adults. And the tongue is what makes them so cool to look at. Some like being handled, others are fussy. Some are lazy couch potatoes, others are more curious and wants to come out and explore. Price range from $175 to $2000+ depending on species, morph, age and whether it is an import or not (get captive bred). Initial cost including lighting is pricey but once all set up, the rest is easy and affordable. And they don't live as long as a boa... Only about 15-20 years.