J.G.
K.,
I also have a son who wet the bed only at night after he was potty trained, almost every night for awhile and then less frequently as he got older. He is now 8 1/2 and has just started being dry every night. He has two older siblings who never wet the bed.
I was worried and talked to the pediatrician, but he was not too concerned, so I decided not to worry about it. It's always a good idea to rule out any medical issues. My son is also a heavy sleeper - sometimes in the morning his bed would be wet and he didn't even know he had wet the bed! We followed all the same advice that you've been given - no liquids after 6, go to the bathroom right before bed, limit acidic drinks and soft drinks - but it didn't help.
We just had him wear pull-ups at night and didn't make a big deal of it. Notice at the store all of the large sizes they carry now - it's not an uncommon problem, and wearing pull-ups is so much less stressful than changing sheets most nights. He even took them with him to spend the night with friends and to camp. He took his cues from us and didn't fret about it.
I know sometimes bedwetting can be hereditary and his dad's brother wet the bed until he was 10. I think as long as you are low key about it and let him know there is nothing wrong with him, he will handle it fine until he outgrows it.
Good luck!
J.