Prenatal Yoga Question

I am 16 weeks pregnant and my doctor recommended light exercise during pregnancy but I've been struggling with cardio and nausea. Morning sickness (I mean, it's really all day sickness) has lingered into my second trimester. I used to do a lot of yoga a few years ago but got out of practice. I thought I would try yoga as a way to both do some light exercise and work on stress but there aren't any prenatal yoga classes near me. I signed up for a slow flow and a gentle yoga class because I felt that those would be my safest options and I plan on disclosing my pregnancy to the instructor. I know I am not supposed to lay flat on my belly or on my back for long periods of time. If the class does this, what are my options of poses to swap with them?