How to save 500$ on a mattress?

I'm starting to become an expert with mattresses. I have 3 rooms that I furnished with Airbnb. I have my opinion and multiple opinions from all my guests. And I can say surely one thing for sure, never buy any mattress from any store. These stores have huge markup and very high operating expenses. In fact, the selling techniques used in those mattress store is very is similar to used car.

The solution?
Free shipping with Amazon. It's even cheaper just to move, throw away your old mattress and get an new one at your new address (free shipping) with Amazon.

Here's the mattress I'm currently sleeping on:

A cheaper option but still good is this one. At 150$ for a Queen size, 8-inch mattress, this is really a no-brainer. I use this mattress in my Airbnb and the reviews are amazing. I love it, I slept a few times on it as well.

How do I come up with 500$? If I look at an equivalent mattress at a mattress store, it costs about 599$, plus there is a 120$ delivery fee. Compared with my 159$ mattress with free shipping, I don't understand why someone would bother going to a store for getting a mattress.