you can always just transcribe hex, or bech32 - for hex you might want to add a CRC32 suffix check string, bech32 includes one
Discussion
I’m considering doing xprvs
so, a HD seed
i still think you should use a crc32 check, and hex, to make the decoder simple as possible... base32 and base64 are shit in this respect
you could make a simpified 256 word dictionary mnemonic key scheme too, that would be 32 words, plus another 4 for your CRC check or 36 words, they could all be precisely 4 letters long to make storage neat
xprvs are neat but they use the crappy base58check encoding
in the end it’s 64 bytes, so why not bech32m