Thanks so much for the replies, much appreciated.

I finally got through on the Live Chat function to ask about our options with such a long layover but they didn't offer much in the way of reassurance.

I was told to go to the transfer desk and request a hotel, 'if they were open' when we landed. I think it might just save a lot of stress to book and pay for a hotel ourselves.

I also asked if we could just check our bags from Edinburgh to Helsinki (and then re-check in for to travel to Bangkok the next day), as we would need some stuff for that one night but the agent I chatted with was unsure.

Thanks again!