How do I choose a formula?

Kate

My almost 8 month old is my third child and I have exclusively breastfed all three. However I will be returning to work and I am completely overwhelmed with how to pump enough when I leave her. If I feed her first and then pump I only get 2-4 oz and if I pump first then I feel like she is hungry at her next feeding. I also can only pump when she is napping and I usually use that time to shower/eat/get things done. Plus I feel like I need to pump a few days in a row to get enough to last her just for two feedings. And then to pump while at work seems like such an inconvenience. I work for a small company so I’d end up pumping in the bathroom. Ugh. So I am begrudgingly thinking about supplementing with formula when I am away but I honestly have no idea how people choose a formula. Just go to the formula isle and randomly choose one? They are like $25-$30 each so if she doesn’t like it or it doesn’t agree with her tummy it’s just a loss. Help me mommas!!!