Hey, for a shopify mattress store, link building needs to be very specific, the best approach is to divide the strategy into two fronts, local links and national authority links, for local links, the key is to partner with local businesses that aren't direct competitors, you can contact furniture stores, physiotherapy clinics, or interior design studios and offer to exchange articles on their blogs, local directories like the Ccamber of commerce or news sites in your city are also a goldmine because google highly values geographic relevance when someone searches for mattresses near them.
To truly scale your business, the proven path is digital public relations, the most impactful links come from media outlets specializing in health, home decor, and sustainability, create content with factual data, such as guides to the best mattress for back pain, and offer it to journalists so they can cite you as an expert source, if you can get a reputable publication to mention your store, that single link is worth more than a hundred low quality ones.