Started my son on semi-solids when he was 6 months old (he's also on TBF, direct latch). When first starting, it's just a taste test, about one teaspoon of baby cereal mixed with EBM. If no allergy and baby can accept, then slowly increase amount. No hurry to increase amount actually since breast milk is still the main source of food whereas semi-solids are supplementary before 1 year old. Probably you can start with more EBM since he likes taste of breast milk, i.e. very runny texture. Try letting him hold a spoon/bowl while you feed him (it works for my son).
For brand of cereal, I go for Healthy Times (found in most big NTUC), Happybellies, Organix, Earth's Best (these are from organic shops). All these are plain (no sugar added) goes well with breast milk which is already sweet. There are many types of cereal to try like white rice, brown rice, subsequently oatmeal, barley, multi-grain, spelt, millet etc. Can also try suitable first foods like puree sweet potato, pumpkin etc mixed with EBM. Just remember to apply 4-day wait rule before trying another new food.
No pressure about introducing semi-solids from grandparents since breast milk is best before 1 year old.