You could technically create a customized word list containing an arbitrary number of words and then use the Electrum mnemonic algorithm to create your seed phrase using that particular word list. It should have the same security level since Electrum still creates a random entropy and encodes that using the custom word list.
Keep in mind that if your list is small (like 10 words), your mnemonic length would be massive since each word encodes a much smaller number of bits.
Also remember that you should also store the list alongside the mnemonic otherwise you won't be able to recover your keys.

FWIW mnemonic algorithm, despite what the name may sound like, is not created for memorization. Its main purpose is for you to be able to write it down (with pen and paper) with a very low chance of mistakes.