what is up with them. I wake up in pain every day.
How have you learned to live with sleeping on a slab of concrete? Or do you like the hard beds? And, as a point of personal interest, how tall are you? My working hypothesis is that they are better suited to shorter people.
My wife and I are the reverse.
We hate soft bed mattresses.
Wake up with aching backs.
I solved it by buying a good mattress topper from ikea. now, I have a mattress from ikea and sold the mattress topper.
They’re good for heavier people. I’m 450lbs and if I sleep on a soft mattress, it creates sort of a canyon into which my wife, to her great dismay, gets sucked whenever I turn. A slab of concrete doesn’t usually create this sort of problems.
Note that the pain will go away over time. Give it 3-5 years and you can’t go back to soft mattresses.
I weigh about 43kg after a big meal and can sleep pretty comfortably on just about any flat or semi flat surface. Soft mattress, firm mattress, couch, bean bag, yoga mat spread on the floor…all good.
Just do what @Aikaili did and get yourself a squishy, foamy mattress topper.
Living in the dorms taught me to sleep on a plank of wood. Working late shifts taught me to sleep anywhere.
Second the IKEA idea. Though I think it might be a bit crowded these days.
Warning about IKEA mattresses. They are an odd size and finding sheets to cover them properly is almost impossible outside of IKEA.
You can also get mattress covers pad things at Costco.
I believe those hard rocks rot less faster than soft ones in the humid weather…
Have you tried shaving them? 
Ikea mattresses are not odd sizes. Taiwan made and sold are odd sizes, like 188cm x 90/100/140/150/180 cm (fengshui mattresses)? You can even find 210 cm in lenght.
Ikea has western standard sizes. (200 cm x 90 cm, 200 cm x 140 cm, 200 cm x 180 cm).
What you need to watch out for is the height/thickness (26-32-36 cm). You always can buy a medium or hard mattress and put a (soft)topper.
Really? I can find suitably sized sheets for my Ikea mattress at both Nitori and Muji. They aren’t a perfect fit, usually they’re a bit too big, but they work just fine. I’ve come across a random fitted sheet at Carrefour, as well, that actually fits my mattress exactly.
I’ve also had no problems getting linens for my IKEA mattress. I’ve bought them from Carrefour and Costco. Pretty sure mine is 150 x 200 cm.
I’m 183cm and weigh just over 95kg. Wife likes the bed a little softer, I actually prefer the hard beds although it can take some getting used to (I have a softer Tempur-pedic mattress back in the US).
Taiwan size is different than Western size. Actually it’s true for most Asian countries where the king size only goes 188 in length. I got mine custom made in taiwan and Malaysia to fit me. You do have to find western size sheets or you have to have the sheets tailored or custom made like me.
I slept on a hard bed in China. But I was younger and didn’t have much issues plus I was sleeping alone. Once you get used to it, not bad for your back. You might be sore in if you sleep the wrong way however in the beginning.
Can’t stand a soft mattress anymore after years on a roll-up bed on the floor in Taiwan and then moving up to hard mattresses. Nothing more comfortable.
There is a difference between a hard mattress on a spring box and the same on a wooden bed box.
Man I used to be hard pressed on getting hard mattresses everywhere I went.
These days though, you either get a mattress pad or go with a soft mattress. I think university did it to me, those beds were notoriously uncomfortable.
Sounds like a Queen size, 152.5 x 203.5. If you are actually 150 x 200 its no wonder the covers dont fit.
Memory foam type of mattresses are IMO great, they are both firm, a little give but dont have the problems soft mattresses have with indentations. In reality, they are not perfect and still need rotation after a year or two.
This is my biggest issue. I rather sleep on a hard mattress than one with a dent. It destroys my back, I always try to get a memory foam cover on top and try not to cheap out on the mattress.