We spend a third of our lives asleep, and ensuring we get a good quality slumber can reduce stress levels, improve our memory and generally make us feel happier. In fact, the physical and mental benefits are tenfold. Our sleep is worth investing in, and a mattress is often a good place to start – but these can come at a cost. Fortunately, Simba's Black Friday sale is here, so you can make big savings on creating a quality sleep sanctuary.