I switched to SPDs a year ago, by buying a pair of cheapish Bikehut flat pedals with an SPD clip on one side. I used them on trail rides until I'd got used to unclipping. It takes surprisingly little time to automatically unclip as you roll to a stop. In fact, I never had a fall from failing to unclip while I was learning to use them.
After the Bikehuts, I bought Shimano's 505 full-SPD pedals and would the adjusters nearly all the way out to make it easier to clip in and out. Now I'm on Shimano's 540s on the dirt and 105s on the road and find it almost impossible to go back to flat pedals. You don't realise how much you start to use all the muscle groups in your legs. Going back to flats has your foot lifting off the pedal at the top of the stroke and sliding around.
Experiment a little with cleat position and angle. Your knees like your feet to be at a certain angle (ie you might normally ride a bit toe-in or toe-out) on the pedal and it's best to try and replicate that when you fix your cleats.