brockly Your problem with trigger pull is a head game and shooting any trigger type you should be able to come to master it with practice. Just give it time and rounds down range and all will be fine. The m&p9c is a good pistol and a good choice as a first centerfire pistol.
Your question about will a .22lr help , heck yes and with M&P having a 22 version it would be a prefect match for cheaper practice and the lighter recoil. That should allow for more shooting and help you learn that trigger control easier.
I cc a kahrs , wife has a m&p9c as one of her rotations . I don't have a problem with any trigger pull type so long as its smooth. .