My boys were almost sitting alone when we started blw at 6.5months. They could sit with a little support.
Its good to remember that milk is higher in calories than the little solids their tummies can hold.
Id wait as it sounds like you want to.
We offered a couple of times a week from 6 months and they took a bit of practice to be able to get the food to their mouth but when they did it alone we knew it was cos they were ready