I use "NFC Tools" to write the URL, which I copy the album/song URL from Spotify and embed it. When I hold my phone near it, the URL appears in the notifications, and clicking it opens it in Spotify, which then starts playing it. I have a bag of 100 tags I got from a friend so no shortage there.

https://apps.apple.com/us/app/nfc-tools/id1252962749 is the one I use.

Yep, that's the one! Very simple to use

Love the simplicity of this. Out of interest, do you trigger just the web player or is there a URL pattern that can launch onto a specific device?

The regular https://open.spotify.com URL is registered to be handled by the Spotify app on iOS devices, so no bouncing from Safari - it opens straight away in Spotify. Nothing to play on a specific speaker, though - but my homepod mini is nearby so a tap to my poster then a tap to my speaker starts my listening session.

Makes sense, cheers. Might give it a go

I have NFC Tools Pro from these guys, https://www.wakdev.com/en/ (but affiliated); I'm assuming you're referring to them. They're on Google Play store too.