I first took Mary Beth's Mommy & Me Yoga xx years ago. Now I'm back after an intro class. This is a very comfortable place to practice yoga. If you have injuries or medical problems, the intro and gentle classes are excellent. Weight and dress are also not an issue which contribute to yoga's stress relief benefits.
Heidi's intro classes are great (and not too big). But maybe you should try another teacher when you're done with intro; Heidi's other classes tend to fill up . . .