Me and my friend both foster and take kids to lots of soft play centres so will list what our fav features are:
Separate area for under twos. With a high gate so that parents can open and close it and can't be reached by older children. (It's horrible when you have a newly walking baby and older ones push them out of the way to get to the toys for little ones!)
Comfy sofas and clear view of play areas
One play centre we go to charge £1.50 per adult but give you a ticket for free tea/coffee.
Good food, we go in the morning and love a bacon/sausage sandwich. Lunch times we like baguettes/wraps.
Dairy free options, my little one is df and it's hard to find a decent dinner for her that isn't just a not sure answer.
Kids especially love ball pit areas and get excited when they have a ball blower.
One playcentre offered free squash for the kids.
Term time toddler sessions, one we go to charge £2.25 during term time school times.
Another centre we go to offer a snack plate which has cucumber cheese tomatoes etc.
Clean toilets and a small toilet and low sink for the children to use. Decent baby changing facilities. A proper changing table instead of one of the fold down ones.
Hope this helps and best of luck with your new venture 😁