You need a /48 (or /56) if you want to do your own subnetting and keep using SLAAC (which is the default way for assigning v6 addresses and detecting address conflicts).
A /64 is not enough for that. You can still create your own subnets, but you will be on your own with address assignment
BellAliant in eastern Canada, the only provider of residential layer 1 fiber in my area, still isn't even assigning a /128 or /64, let alone proper delegation.
A /64 is not enough for that. You can still create your own subnets, but you will be on your own with address assignment