i am pretty muck new to knitting. i recently shopped for baby pattern book online and turns out most of the item fits only up to 12m. i was looking to knit for 12-18m. it's only one size up, but i am not very good at improvising and worried that the shoulders and hips might be too tight even if i can elongate the sleeves and the hems. is there a certain calculation to enlarge patterns for bigger kids? can i use slightly heavier yarn and fatter needles to bring it one size up? i want to knit jackets, sweaters, and rompers.