I don't have shoe recommendations but did want to suggest wearing a belly band, that can help to support your growing belly so your back hurts less. I got one at motherhood maternity for $20.
I teach middle school and also went back last week. I live in flip flops as I am 32 weeks and can't tie my shoes/struggle with socks. I also have a few 'teacher'chairs that I rotate between sitting in as I teach and work at the board and my desk. Having an ottoman) or even a sturdy cardboard box) under your desk to prop up your feet when you can helps too. I feel your pain though. By the end of the day I am exhausted.
I love flip flops also but I've been reading (which I am in shock) that they r actually not recommended for during pregnancy. Since they r flat n ur body center of gravity changed it adds to ur back aches n pains. Sneakers would be better for u. Any she that has a small heal or isnot completely flat are better. I'm still wearing very comfortable platforms but they just have a small rise.
The maternity belts work very well for me! Give that a try?
Arent tennis shoes went too? I don't understand how one is different from the other. At this point if I'm comfortable I'm wearing it lol