You can do it. Designing your own knit pattern that is. It's not difficult at all. Okey maybe it's not beginner level knitting, but not far.
You only need cross ruled paper (not necessarily sponsored), test knits, some common sence and a grafical calculator.
Kidding! regular calculator will do. Draw the whole pattern on a cross ruled paper. If it's a small pattern you can assume that
the hight and the width of the stitch are equal, but if you want a bigger pattern you should check from your test knit what is the ratio between the hight and the width of the stitch. Therefore you will have to draw your pattern to appear quite long on the paper. In the knit it will look normal. You could also make a grid with excel that has the correct ratio and design the pattern on it.
Divide the total amount of the stitches on your knit with the amount on the pattern, you should end up with an even number, but most likely you wont. Then find out what is the closest amount of stitches that would give an even number. Adding a few stiches or removing some wont affect much on the size of your finished knit. Unless it's like really tiny, like a baby mitten.
By the way, yesterday I saw on the pharmacy a woman that knit, she was about my age. That was so cool, but not that rare. But few years back I saw in a bus a girl that was making a cross stitch, that was even cooler.