Ideally,as your doctor said,solids are started after 6 completed months because baby will not be physically ready before that.
Signs of readiness are:
Neck control
Ability to sit with/without support
Loss of tongue thrust reflex( baby pushes food out)
However,as you seem keen to continue:
Homemade solids are better than high
sugar ready made baby food.
You can give rice,rahi,dal,pureed vegetable or fruit minus salt/sweetener.
Offer once a day only until baby is 6 months old,and gradually increase volume offered.
Continue breastfeeding--this meets most of your baby's needs right now.