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
A /64 is not enough for that. You can still create your own subnets, but you will be on your own with address assignment