Mattress shops are generally made by agents, so it depends on the strength of your agent and the attitude of your boss.
If you want to do it, you must first understand the mattress market, different brands, different grades and different product classifications. Some of them specialize in latex, some make brown mats, and most of them are springs and sponges, which is what we often call Simmons mattresses.
Then you should know about furniture, and you should help others improve their homes when they buy mattresses, showing your professionalism.
You also need to know how big a mattress can fit in a room, and you can also help customers make a simple plan for the bedroom.
According to what you said, the basic salary is low and the commission is earned by sales. Every boss is different and his salary is different. There are also regional differences, and big cities will be higher.