Hello Sanjaya - Welcome to thalpal.
Today Thalassemia prognosis has changed a lot. People are liviing in their 60s with proper management and living normal life. They are marrying, having their own biological children and living a normal life. Please enjoy your child and don't treat him any different because of Thalassemia.
Coming to your question - There is no need to worry too much about what food to give him. Breast milk is the best source for getting all the nutrients. For external food - as you are already giving the boiled vegetables, daal-rice are excellent. Don't worry too much about the contents of all food because the child needs to nutrients for all types of food.
Do let us know if you have more questions. There are hundreds of thals on this site that can share their experience with you.