Honestly,
From what you describe I don't think you need any type of attachment to your pedal at all. I doubt you'll ever ride a stretch long enough on a bike trail dodging pedestrians and dog walkers to utilize an upstroke for pedalling. And if you're not riding uphills and downhills, you really don't need to worry about your feet slipping off the pedals.
I would recommend that you just remove the clips from your existing pedals or buy a cheapo pair of platforms at your local bike shop. When you decide to move into serious single track ... OR ... you start pounding out 30-40 mile road rides, then you might benefit from being attached to the pedals.