Best to consult online for detailed and customised counselling

Start with mashed rice with boiled or fried potatoes , thick dal with ghee in it, cooked vegetables , green leafy vegetables , carrot , sweet potato , beetroot etc ..Initially feed two three spoons slow increase to half katori . Can give papaya , cheeku and bananas at evening time and apple and carrot steamed in form of puree..

Refer to IYCF guidelines available free online which is approved by WHO and IAP. As general guidelines One to one discussion is needed to assess your child and advise accordingly

Consult with Pediatrician physically for further evaluation and treatment

At 6 months of age you should start complementary feeds. High chair is not necessary but helps to establish a routine and a practice to sit and eat at one place keeping food in plate. It's one sort of conditioning. Start with fruits or vegetables in mashed puree form with 2-3 spoons a day. Increase the frequency and amount gradually. Give the same fruit or vegetable for atleast 2-3 days to assess allergy.