When we needed to bring formula on the cruise we bought the pre made nursette bottles, like the ones you get in the hospital. There was no need to worry about keeping them cold as they store at room temp. I dont know if they make the special formulas in that form, but if so, I would recommend getting those. The convenience of not having to mix, measure, wash, keep cold, heat up,etc... was well worth the extra cost.
Good luck!