USA models are different than England's, so I can't help with that. I do know you want a 12mm collet. You can usually find a collet for the same model for the smaller shank bits. But a full sized router is pretty powerful and the larger diameter shank is a better choice, especially for larger bits.
Here is a chart that shows the profile cut of the most often used router bits. I find this chart to be helpful.
Here is a chart that shows the profile cut of the most often used router bits. I find this chart to be helpful.