You could try larger needles, size 13 and 15 instead. Or look at the stitch increments between sizes and go up one or 2 more 'sizes', whatever you need for the finished measurement you want. So if the CO sts are 4 more for each size, CO 4 or 8 more. Look at all the st numbers - for the sleeves, the decs at the underarm and after decs, incs etc. The length of the body, sleeves and armholes will be given in inches, so work them to the length you need (which may be the same as one of the actual sizes on the pattern, unless you're a lot taller/longer too).
sue- knitting heretic