It's normal for babies this age to have night feed so I'd just follow your baby's lead for now. When you wean you can swap this for water as anything other than breastmilk at night will damage his teeth.
Breastmilk or formula should be your baby's main source of nutrition until at least 12mo so if you choose to stop breastfeeding at 11mo you would ideally need to give formula until he turns 1yo. If you wean after 12mo you could just switch to solids and skip introducing the formula and then having to wean it shortly after, especially if you plan on using bottles.
Please let is know if you would like help with weaning, whenever you chose to do it 🙂 Just remember to do it slowly so your body has time to adjust and you avoid blocked ducts and possible mastitis.
Good luck
