Hi muyem,
Most of the better manufacturers or retailers don’t have or need “fake” sales and sell their mattresses at the same great value every day of the year. Post #5 here may also be worth reading.
Of course as LEW mentioned you can always call them as well.
Whoever was telling you to wait for sales will probably also tell you to shop for major brands at chain stores and make the same mattress shopping mistakes that most consumers are already making.
I would start with post #1 here which will give you all the information, steps, and guidelines you will need to make a great choice … no matter what time of the year it may be.
Phoenix