Write your seed phrase on two pieces of good paper, with good ink. Double check both of them for accuracy. Then triple check. Next, store them securely (well hidden) in geographically separate locations, in case of fire, flood, tornado, volcano, etc. Write a somewhat cryptic note to yourself to remind you where you hid the papers. Consider storing each paper in water-tight plastic (eg, ziploc bag) in case the hiding place gets wet (a pipe breaks, roof leaks, etc.) or to thwart insects from literally eating holes in the paper. Check on each of them, from time to time, just in case.
In ADDITION to that (not "instead of"), memorize your seed phrase. It isn't difficult at all. For example, quietly recite it to yourself every time you take a shit, from now on. Better to have it (memorized) and not need it than to need it and not have it.
There are other excellent ideas for storing a backup of your seed phrase (one, for example, involves using a punch to hammer a morse-code-like message into something more or less permanent).
There are very serious risks with using Bitcoin custodians.
Reminder: Back up your seed phrase.
from Bitcoin – The Currency of the Internet