I don't have any specific model advice. I hauled my kids AND groceries around in secondhand Burleys. If you can find one, it might be worth paying more because their customer service is so good. If you have a problem with your used trailer, they will promptly advise you.
As far as modification, at least with my Burleys the mesh seats were removable. But I liked to use them for more delicate groceries when I shopped alone. YMMV.