Do you own a trainer? If so, put your bicycle up on the trainer and practice clipping in and out. While you are doing that, if you find you are still having difficulty, make some adjustments to your pedals to make them looser.

BTW - I've got mtn bike shoes, and the SPD pedals, and they are just fine for clipping in and out ... I've got literally thousands of kilometers with the pedals and shoes, and I've clipped in and out probably thousands of times too. I've never heard of someone needing stiffer soles to make that process easier!! All I had to do was to loosen off one screw. You can get them so loose you're almost stepping out of them ... and then you need to tighten them just a little bit.

My mtn bike shoes are also much easier to walk around in than my roadie shoes ever were.