My opinion is that if he is six months old, he will start to need to try some new foods, so I say start with some cereals, veggies and fruits. You can either make your own or buy them ready made at the supermarkets, you can of course still breastfeed for as long as you like, but I think that at six months, starting solids is a good option. Again, don't stop breastfeeding, sounds like thats working really brilliantly for you! Keep up the good work!
If I recall correctly, you can give him solids AM & PM for a while, like breakfast and dinner, and bf when you feel like it, and in a month or two, build up to three meals a day! Let us know how he gets on! Its a really fun time when you start solids with a little one!!!