First of all- Breastfeeding your son is wonderful and gives him all the nutrients he needs. Don't let anyone make you feel like you need to stop or you're not giving him what he needs.
As for Solids- We started with Carrots. We fed them once a day (one oz) for 4 days, then we went to sweet potatoes, then apples, bananas, and butternut squash. We also do mixes with him. Butternut squash and apples, sweet potatoes and apples, sweet potatoes and squash, apples and bananas. This week were going to start the green foods, like peas.
Good first foods are avocados, bananas, carrots, and sweet potatoes. =)
Check out http://wholesomebabyfood.momtastic.com/! Thats a great source of info on starting solids and how to make them yourself if you're interested in that! (its a huge money saver!)
Good luck! =)