I don’t want my heroes to have to deal with quotidian grownup issues like paying the mortgage, having to work overtime,

They don’t have to; most of the time their jobs aren’t even really important to the overall story; they’re just there to explain what they do during the day or just to have another setting. And as for paying the mortgage, you don’t have to go into detail about that or show it; just give the character some “easy” or “explainable” day job and have them live a middle- or middle-upper-class lifestyle, and you’re good.