Most people rave about knots. They're not really my thing (think of it as a wide part near your opening) but they are a good way to add girth. Durka or Boxie might be up your alley: big knot, small shaft. If you're not sure, go for Boxie as it's less to sink into an "experiment" than Durka is and it has a wider knot than the comparably priced Ruff JR.
Every horse but little rider generally has a thick shaft with a little bit wider at the tip and mid ring. It also gets wider the further down the shaft you go, unlike the canines that have a "break" with a thinner part near the base. I don't own one yet (waiting on Bear to make my order!) but it does look fun and like an easy transition if you're used to humans with their thick shafts and slightly wider heads. I'd say try Lucas or Oscar, whichever has the measurements you like best.
You might like playing with Bear Essentials (it's sort of like a ring-free horse with an oval-shaped shaft) as well. It's pretty girthy with a fairly short shaft. I have not tried one, but I have not seen anyone ever get rid of one if it helps!
Toys that are mostly length: Gryphon, tentacle, Lil' Rider, Leo's Lance, Darius, most of the training toys. Leo/Darius are very human in proportions, the rest tend to be wider with proportionate length.