MIEventer - I started with working on flexion, lateral first and then vertical, as well as doing lots of transitions to get him listening to my leg, and I do this in our warm ups as well, on a loose rein. When I actually ask, I take up a contact, not a very tight one, and then try and get him going forward and tracking up, using lots of inside leg to outside rein, while asking for a little flexion from the inside rein. I know that collection isn't just the headset, it's about the back and hind-quarters as well, and I know that our "collection" is probably far from perfect, but it's a start.
We've been having lessons and working on this with an instructor, but due to numerous cicumstances we haven't had one in about 2 months, aside from Pony Club, and I hope to get back into a regular lessons soon.
Good for you :) Sounds like you are doing things right. Just take it slow - he is green. My TB has been off all winter due to corrective shoeing - we started to get back into work, until he decided to choke on me last weekend - so we're off again....BUT when we get back into the swing of things *knock on wood* we'll be doing lots of forward work, allowing him to search for the contact.
Weak muscles will become strong over time :) Just be paitent.
I had a good collection of Myler Bits. I was lucky to of found mine over time at tack sales. I got a bunch of mine for $10.00 each - if you look hard enough, you'll find them at great prices used.
You don't have to buy brand new.
I sold a bunch of them, and have 2 left. They are both Level 1's - Comfort Snaffle.
Level 1's were designed for horses like ours - weak muscles, starting to understand the concept of forward movement, back engagement - etc, etc - plus, only the Level 1 Comfort Snaffle Wide Barrel is accepted in the Dressage Ring - so that might help you out decision wise.
I had a Level 3 Low Ported - and it was too much.
If your horse is going great in the bit you have now, I wouldn't change things.
I do love Mylers tough, for the fact that they wonderfully designed with their mouth pieces, and I love that I can pick up one side, without effecting the other.
Have a look around on www.tacktrader.com
and ebay. Also try the Bits and Barter Board - that is a forum where people sell their used tack.