if you're looking to retain articulation, I think fabric/softgoods may be the way to go...
For instance, depending on what you use, the right thickness of fabric could build up the figure where you want "bulk" just right and add a flexible "sleeve" or whatnot to it. I'd glue it in place of course at each spot since it's covering something you don't like, so you wouldn't want to remove it. Some 2-part adhesive would work well for a permanent glue-on.
You could really cover it well with fabric though at the various areas you wanted to. Like make maybe a "bell-bottom" to the pants by sewing a conical shape that you glue up towards the bottom of the knee joint, and the fabric sort of lays on the foot... You'd have to paint the legs to match the fabric in color but that's not as huge a deal really.
Something similar could bulk up the shoulders, and a wrapped scarf with a thinner fabric could be made any color you wanted and would hang on the neck well while moving with all joints on the figure itself.
Just some thoughts from my end, but I'm a fan of using cloth on figures to retain poseability too so I'm biased.