|I would not bother with anything for the diapers. You can really minimize stains and help with poop cleanup by using fleece liners, but in your case, you should probably be careful with that, given your concern about polyester. Maybe something to experiment with someday once you're up and running and have only that one variable.
Poop stains aren't the prettiest to look at, but diapers are what they are, and stains don't mean they aren't clean. My advice would just be to live with stains, but if you can hang your diapers in the sun to dry (even through a window can help), the UV rays will make breastfed-poop stains disappear, and can really lighten the tougher "regular" poop stains. Straight-up lemon juice on the stains and then drying in the sun can help, too, but that's sure not something I'd bother with regularly.
As far as clothes go, I have to say that I don't generally bother with stain removal, figuring that things will work out in the wash over time (but I line-dry almost everything and wash most things on cold, so also am not setting stains). I wonder if Method would make something that might work for you?
As a side note, not to complicate things too much for you, but just so it's out there, some kids have reactions to detergents with enzymes in them (and most main-line detergents do have enzymes). Most kids are fine with these, but some kids don't do so well, getting irritated skin, and this can show up esp. in the diaper area. If your son tolerates Tide Free on his clothes, chances are it will be fine for his diapers, too, but just mentioning it in case it's relevant at some point. In Europe detergents are sold "bio" and "non-bio" (with or without enzymes) and the non-bio is what's recommended for use with children. I didn't even know that enzymes were used in detergents or could be an issue for some kids until I was trying to figure out the detergent types when we moved to the UK a few years back.