Last weekend I finally got out again to a few thrift stores, to look for new used clothes for myself. What I mostly bought were used things that I could make new clothes from: a tablecloth, a fabric shower curtain, a knit shirt several sizes too big, and a blouse that needs new buttons and perhaps to be overdyed. I also found a short corduroy jacket and men's pajama pants (which have a drawstring and can accommodate a third-trimester pot belly) that are fine for me as is. I stopped at the art store and bought fabric dye, for dyeing fabric that I already had.
Over time, I have worked out a few clothing patterns that suit me well: a simple skirt pattern in a comfortable length, a long-sleeved T-shirt pattern, and a pants pattern. I based these on items that fit me well, and on my own measurements, with some calculation. A lot of modern clothing is very simple in construction (and skimpy in fabric, hence the tablecloth and curtain), so I find that I can sew my own clothing fairly well, if I don't try to duplicate the detailed finishing that is available commercially.
With my custom patterns and the fabrics that I bought, the rest was just work. So the tablecloth and shower curtain have already become skirts, the knit shirt now fits (although the stitching looks a bit awkward because I pulled the fabric too much while sewing), and so does another shirt that I already had. I am currently working on another skirt, using a thrifted sheet that I am embroidering with crochet cotton and will be dyeing.
Sewing hints: I usually do half-inch seam allowances. For the woven fabrics, I edge stitch around each piece before sewing them together, with a narrow zigzag stitch. For knits, I use a wider zigzag stitch for all the seams, with a ball-point needle to avoid breaking threads in the fabric. I often do some of the finishing work by hand, and sometimes all of the stitching; knits are especially forgiving of hand stitching (see Alabama Chanin). I buy thread by the cone, preferably second-hand, and just put the cone on the machine and set the thread tension as low as I can--I have an older sewing machine with metal parts, which will take that sort of abuse, but newer machines might not, so be advised.