Hello there. I completely understand your frustration with store-bought bread going stale or molding so quickly. To answer your question, you should look for authentic sourdough bread at the market.
Sourdough naturally stays fresh much longer because of the natural fermentation process. The lactic and acetic acids produced by the wild yeast and bacteria create an environment where mold cannot easily grow, all without any chemical preservatives. Furthermore, its dense crumb and crust retain moisture better than standard sandwich loaves. When buying, just check the ingredient list to ensure it only contains flour, water, salt, and starter.