Is there a way to convert my regular toilet seat to one that's like a Toto...so the seat won't slam shut?
Buy a new toilet seat. The big box stores sell several that are billed as "Whisper Close" "SlowClose", etc. We're talking $30-40 here (as opposed to $10-20 for a low-end toilet seat) so it's not like I'd be concerned with preserving the existing seat.