Western bridle type for a draft horse that also drives

I just recently purchased a Belgian mare that is trained to ride and drive. When I asked her owner what type of bit he used on her, he said snaffle. He indicated to me that she is not trained to neck rein, only direct rein because she drives. I have purchased a draft bridle and measured her for a snaffle bit, but during my research I found a side pull bridle. What exactly is this and is this what I should get for her instead of a regular Western bridle?
Thanks.
Maureen

This is a sidepull- Google Image Result for http://www.fourwinds.net/accessor/aimg/jt539072.jpg

Which, as you can see, is a variety of bitless bridle. If your horse isn't used to riding bitless, I suggest you try this option in an enclosed area first, such as an arena or empty paddock. I also suggest that you get a sidepull with a flat noseband instead of the waxed cord that I posted.

However, if you choose to keep your horse bitted, just find a nice sturdy bridle that fits, and preferably something with removeable blinkers for when you want to drive her. Like this:

Google Image Result for http://catalogue.vdkwp.com/images/harness_spotted_work_2.jpg

Best of luck.

Thanks aspin231. The information and links were very informative. Glad I asked the question before I purchased anything. We rode my Belgian mare Miss Kitty for just a few minutes tonight bareback with just a halter and a couple of lead ropes in an arena and she did pretty good. Don't have a lot of information on her background, so have no idea how long it had been since she had been ridden. I've got a draft bridle and a couple of snaffle bits on order so will keep you posted on my progress. Thanks again for the help.
Maureen