weaning help

My son will be 13 weeks on Wednesday and over past few days we have tried him on baby porridge. Jus a couple of teaspoonfuls after his bottle but he opens his mouth looking for more. He has struggled with bad trapped gas and reflux since birth no matter what we have done. As a result he is really small still in up to 1month clothes and size 1 nappies. Not looking for judgement I know guidelines say older. Just wondering if any mums have experience of early weaning, foods, quantities or can offer any help to a Ftm. My lil dude much happier after a feed with solids after.