Write the next sentence in the following story.

How to choose a mattress when you have back problems 
Learn about mattress firmness ratings. 
There's no definitive, industry-wide scale for mattress firmness. However, you'll find most mattresses labeled on a scale from extra-firm to extra-plush.

OPTIONS:
- Mattresses rated for firmness are usually made of foam, cotton, and silk. Bump mattresses feel more firm when they aren't moving.
- Each mattress has unique mattress recommendations, as do larger, heavier mattresses. Determine how often you will use a mattress and if you use it as soon as possible.
- Your ideal mattress firmness should be somewhere in the middle of this scale. Mattress firmness scales aren't uniform across all manufacturers, so ask a store salesperson if their mattresses typically run softer or firmer.
- Fitted mattresses typically have a rating ranging from these-0 to 255. Mattresses containing a higher rating will usually produce heavier mattresses, while mattresses with a lower rating will produce heavier ones.
Your ideal mattress firmness should be somewhere in the middle of this scale. Mattress firmness scales aren't uniform across all manufacturers, so ask a store salesperson if their mattresses typically run softer or firmer.