Modifying a bootie pattern

I am knitting Saartje’s bootees for a gift using this
pattern, which says makes less seams

The origanal pattern uses Rowan’s "Cashcotton a fingering weight 35% cotton, 25% nylon, 18% angora, 13% rayon and 9% cashmere, , size US 1 or 2 needles, 7 spi with 8 garter ridges/inch, and 35 sts make a bootee that is approx. 3 3/4 inches long.

I am using Sirdar Snuggly yarn which is nylon and acrylic with US 4 needle. I knitted a swatch which was about 5 spi with 6 garter
ridges/inch cast on 24sts which measured almost 4 inches.

I need the bootees to fit about a 5 inch foot and am not sure
about the guage and sts to  , inc. and dec. etc to fit the 5 inch size.                                                                                         I able to figure the math out , it seems complex to me.  I know some of you can figure this out, any help would be great