As far as i thought you are talking about private keys that most free quiently you want to hold your boitcoin with safety.So surely i'm not recommened you using coinbase like wallet not only there any private keys but also many more unfair reason it's not insured.
if you want safe in big bitcoin, much bitcoin
you must choose wallet addres is support private key and 100% full control
you can use eleterum or bitcoin core, is the best wallet if you hold big bitcoin
coinbase not recomended hold big bitcoin because not support private key