hi miamimommy, welcome to motheringdotcommune!
I have a feeling your post might be moved to a forum where it will get more of the kind of attention that you are needing to answer your question about your baby's rash.... I know it can be confusing where to put your posts sometimes as there are alot of different topics, aren't there?!? once you get familiar with the different boards, it is so awesome to have such a huge selection when you need help on different issues!
I understand what its like to be worried about diaper rash, believe me i do. My 27 month old dd has schooled me in diaper rash remedies. My ten year old dd never ever had a diaper rash and so i was totally at a loss for experience when my baby turned out to have very sensitive skin.
you said you were looking into cotton diapers (even making them yourself?), can i ask what you are using now? are you full time cloth or do you use disposables at night or even all the time? its pretty unpopular around here, but i feel brave tonight so i will just admit i use pampers cruisers on dd always have. i am a sahm, so i know when we have poop and i never ever let my dd be in a poop diaper. but, there have been times where she was a pooper and i didn't know it..... like when napping. and man, thats where she has gotten some really bad rashes.
sometimes i think her poop almost burns her skin. even if i am right there while she is pooping and i get the diaper right off her, i can see that her little bottom will be red right where the poop touched it! i should buy stock in the Desitin company since i use so much of it. i swear by desitin. not the creamy stuff...it doesn't stick well enough. the original 40% zinc oxide desitin. i might as well put it in a caulking gun because thats how i apply it. i just fill up the butt crack with desitin. up to the top.
i also think that baby wipes can contribute to the problem for my dd. sometimes after poop, i just take her little poop bottom into the bathroom and hang her butt into the sink. once Ive knocked down the big stuff, i use a bar of ivory soap to get her clean then rinse and dry with a soft towel. this keeps the rashes pretty well at bay...... unless she pulls the sneak poop on me (the ones that i cant smell).
anyways, welcome and i hope this helps a little.