I've seen a few older posts here from people asking if Ikea sells Twin XL Beds. If you search Ikea, you won't find any. However, a "Split King" is just two Twin XL beds pushed together. Now, take a look at this: ESPEVÄR Slatted Mattress Base with Legs

It's two Twin XL sized bases, each with its own set of legs. So, Ikea does (kind of) have Twin XL bed frames. If you've got a friend asking you for a ikea twin xl bed frame AND they want two, (or maybe you each want one?) then get the ESPEVÄR Slatted Mattress Base with Legs and there you go: two Twin XL bed frames from Ikea for $155 each ($310 USD)

Now, it's still true that Ikea does NOT sell a mattress in the Twin XL size. If someone comes across a King Mattress that is two Twin XL mattresses inside a big mattress cover, post it here! Otherwise, you're best off getting a Twin XL mattress from Sleep Country or similar.

Ikea USA: https://www.ikea.com/us/en/p/espevaer-slatted-mattress-base-with-legs-dark-gray-s09207888/

Ikea Canada: https://www.ikea.com/ca/en/p/espevaer-slatted-mattress-base-with-legs-dark-gray-s99207879/

PS Here's a cool Ikea hack of the bed: https://www.midmodernmama.com/ikea-hack-espevar-foundation