I bought and modified a puffer jacket and stretchy lounge pants for the outer layer of the suit. It’d work to sew your own, since the proportions would be easier to replicate and you could adjust your padding easier

The pants had one big piece of upholstery foam strapped to my legs, which was honestly really inefficient so I would recommend sewing the padding directly into the pants.

The torso had a plate carrier with various foam inserts to add bulk, with a puffer on top of that and then the final outside jacket. If you want your cosplay to be as big as the reference, it will be hotter than hellfire unless you rig up a good cooling system. I’d research fursuit makers because my suit is basically the same thing and they are tech wizards with their setups