Could we have used the infinitive for "... so I don't catch a cold" ? >> [rendering it as: "... para no coger un resfriado"].
My grammar book (by Butt and Benjamin) implies that 'por' might also be permissible here: i.e. "... por no coger un resfriado" - when it means "out of a wish or a desire to not catch a cold". Thus, I am wondering if [when a negative is involved] - "por no ... +infinitive" might actually be more common than "para no...+ infinitive" ?