The option is rolling out right now, no more workarounds needed
You can just hit the floating action button (FAB) for a new WhatsApp message in the lower right-hand corner. The new option to message yourself should be pinned to the top of your list of contacts. Reassuringly, WhatsApp says this chat with yourself is also end-to-end encrypted.
However, the feature appears to be arriving on devices in a phased manner. So, it could take a few days to show up on your devices. Until then, you could always create a group with one other person, remove them, and use that space to chat with yourself. Perhaps you could still use this option to have two separate chats with yourself, for whatever reason.