That 50 mm lens would be a good choice (most 'standard' lenses are of a double Gauss type design, which performs very well in the close up range, on either side of the 1:1 'mark') , but compared to the minimum amount of extension you get using bellows, 50 mm can be a bit short.

A fixed focal length lens in the 80 - 100 mm range would give you a more usable range, but most already are of a design that holds up less well in the close-up range.

If you are going to shop around and get some new (or new-to-you-used) stuff, a longish macro lens would be the thing to look for.

Or (less expensive) you could use that 50 mm you already have and get some extension tubes for when the bellows is too long.