I always say that the two things you need to exercise are a good pair of shoes and a good sports bra. Of course the problem with bras whilst you’re breastfeeding is changes in boob size and of course the need to access them frequently.
A breastfeeding sports bra can seem like a huge expense so is it really necessary?
This of course all depends on what type of exercise you’re able to make time for. If you’re going to do yoga stretching or any type of slow exercise you may not need to spend the money on expensive sports bra so long as you have a nice supportive maternity bra on nursing bra then you can just wear this to do your exercise,  hell, for this type of exercise, don’t even worry about putting shoes on.
If however you’re going to be doing high-intensity exercise,  which will mean jumping around a lot, you should definitely make sure to encase your breasts in something that puts them as firmly as possible to your chest to avoid damage and any pain.
Breastfeeding right before doing exercise can also help reduce the size trying to pick a time when you’re feeding from both sides so that they feel relatively even. This is not essential though and getting exercise and feeling good about doing exercises your priority.