Tape on diapers are better than Goodnites for bed wetting in older kids, especially if they are heavy wetters.
Tape on diapers can get a better more leak proof fit than the pull up Goodnites can do.
Some kids are fine with wearing the Goodnites and other bed wetting pull ups, but some kids need extra protection and so the tape on diapers can be much better than the Goodnites bed wetting diapers.
My 6 year old son also wets the bed and wears a size 8 parents choice diaper and they fit him just fine.
We tried the Goodnites, but they leaked on him as he's a heavy wetter and the tape on diapers like Parents Choice size 8 diapers work much better for him.
If your 6 year old son is a bit small for the size 8 Parents Choice diapers, you may need to use a size 7 diaper instead like Cuties size 7, Pampers size 7 or even Luvs size 7.
There's also other good brands of size 7 diapers that can fit your 6 year old son.
I used to fit into the old size 6 Pampers when I was a kid and wet the bed, but it can also all depend on the size of the 6 year old and their build.
A size 8 Parents Choice diaper and other size 8 diapers should even fit a 10 to 12 year old if they are of average sized build.
After that, you would likely need to switch to using Youth sized disposable diapers.