I would not recommend a dojo loach for a 45 gallon. They can grow to be a foot long. I'm not sure what a walker goldfish is. Is it a single tail or a fancy? Either way, your tank is pretty well stocked, goldfish need high water volume and lots of space.
A good small bottom dweller that would work in a tank that size and with cold water fish is the bulldog or rubber-lip pleco. I keep one in my 90g with my fancy goldfish. They're pretty shy but once they get used to the other fish and stuff they'll come out and be cute. They like caves. Mine especially loves to hang out in the rock piles. They also like zucchini like bristlenose do, but will eat pretty much anything.
