You got it right, toes should NOT grip. Your feet should be relaxed, transferring the power of your hips, glutes, etc. to the pedals. I wear my mtb shoes to spin class, so can't give a specific recommendation as to shoes. Generally, you want something with a stiff mid-sole/sole and a "walkable" bottom. You can get "spin specific" shoes, but any proper bike shoe with a treaded, not slippery sole will do. That is to say, if you find a pair of mtb shoes on sale that fit, get 'em! Then you have the choice of whether to get cleats or not...a whole other topic.