Didn't read any of the replies.
Do you mean bigger as in thicker, or bigger as in taller?
Not sure on your experience, or what you plan on doing with said horse, but if I were you I would try looking for a seasoned WB or TB, or even a TB cross. Depending what you're looking to do, I'd even recommend a TBxdraft type or Appendix. There are larger TBs out there as well - mine included (17.3h & growing, fairly thick as well). You really just have to look around. You really can't start your search by saying "I'll only get a WB" or "I'll only get a TB" or "I'll only get a horse above x height". Keep an open mind.