Need some serious advice on how to keep white linens and towels white!!

So I work front desk at a very small privately owned motel and I’m also responsible for doing the laundry. We are struggling to even stay afloat right now so we can’t afford any of the extra stain removers and what not from the place that supplies our laundry supplies. We just get the basic detergent/bleach/softeners and that’s about it. I’ve been trying everything I can think of to remove stains and hardly anything is really working. They tend to just buy me some Shout and tell me to figure it out but a single spray bottle of stain treatment does absolutely nothing for the majorly soiled linens. Mind you, they don’t want me throwing anything away. I’ve tried soaking in bleach but that’s literally the worst way to remove stains and just ends up ruining the linens. Please help me! I’m not a laundry attendant and I don’t have anyone who knows what they’re doing to help me out so any help would be so much appreciated!!