Cd/DVD discs are enough for me to hold my coins for the long term.
I have had many CDRs that were useless after a few years. Some are still okay, but I'll always asume they won't last.
M-disc would be a great deal it has 1000yrs of lifespan this would be a nice option if one of your grandchildren is your heir of this backup for future holdings and to later heirs(for new generations). It's not so expensive it's around $80
For long term storage, I trust paper much more than anything digital. My solution for Bitcoin Core's wallet.dat is only to keep it as a hot wallet. I have backups (on external HDD and USB stick, and don't keep much in it.