Adding insulation in a finished ceiling with no access
Sounds like a talk with the condo board is in order. Insulating the space between the floors would be beneficial for everyone, not just you. Cutting a few holes and blowing in cellulose would do a good job. Even better would be filling the space with mineral wool batts which are very good for soundproofing (and could be done as a DIY job) but that would require removing the ceiling drywall or plaster.