Splurging is an interesting concept.
I once read something where the author was suggesting that clothes shopping should be viewed from a dollars per wear perspective. Most evening clothes cost an enormous amount per wear, and she contended that you should get these from an op shop, or buy them in such a way that you could wear them more (for instance, using flashy accessories with clothes you can wear elsewhere), or not bother too much about how long they would last - a poorer quality finish is usually cheaper. On the other hand, clothes you use every day should be better made and perhaps consume more of your clothing budget.
I have since extended this thought to other things. If I’m not sure how much I’ll use something, I might buy the cheapest version of something as a proof of concept, and be prepared to buy for life later.
Given that you only need two sets of sheets, and they should last you at least 20 years, splurging on a fancy set is pretty harmless. It will set you back far less than a daily coffee habit, and it’s by far the smallest cost of changing to a different bed. Obviously, buying white sheets is much more likely to ensure they last for the entire 20 years than if you buy sheets in the latest fashionable colour (and stuff dyed white has a longer life than the same stuff dyed in colours, and is fade resistant). Airing the bed each day after you leave it, and simple ongoing maintenance can also extend the life of every part of the bed.