I'm so glad the dishcloth pattern worked out so well for you!:happydance:
I don't know of anywhere online to get an assortment of all the same sized squares, but if you know how to crochet,or if your Nan does, a SC, ch-3, SC border can be used to join squares that are almost the same size and no one but you would be the wiser about the squares being slightly different sizes.
Or, you may want to look for a Leisure Arts dishcloth pattern booklet. All patterns in those dishcloth booklets tend to have roughly the same dimensions and could be sewn together.
And 20 pence for needles, plus a Nan who can help you learn, is a fabulous deal!