My absolute favourite, favourite piece of workout equipment during pregnancy is the stability ball. I highly recommend every pregnant women gets one! I bought mine on Amazon a few years ago for around $10.
The reason it's so great during pregnancy is because it adds instability to whatever exercise you are doing, which forces you to active your transverse abdominis (TVA)! These are your inner abs that basically act as a girdle, or corset. They hold everything together, support your bump (which helps prevent lower back pain), prevent abdominal separation, support the pelvic floor, help the mid-section return to "normal" after delivery, and prevent that pooch a lot of women struggle with losing postpartum.
Another reason I love using the stability ball is because, when it's time to stop lying on your back during pregnancy, it's a great alternative! You can still do exercises that require you to be on your back (like chest fly, chest press, etc), just on the stability ball instead! The ball will be on your upper back, meaning there isn't pressure on the vena cava vein in your lower back.
I promise the $10 investment in a ball is so worth it, even if you only use it during pregnancy and postpartum!!
Hopefully I've convinced you into getting one now haha. Below are my favourite exercises to do with a stability ball, and are the ones I personally use every week, and the ones I have my clients use every week!