Another option you can try is interparcel. They are a shipping brokerage based in the UK, but I'm pretty sure they do have carriers that do ship from the US.
They will always get you a better shipping price from a carrier than you are able to get yourself by going to them direct.
If you do want to go with a mail forwarder, just Google US Mail Forwarders and you'll find plenty of options to choose from. Just make sure you get a package that suites your requirements.