are there no uniforms commercially available?
Yes. Doesn't mean they always fit better or are made of the right fabric, or have accurate insignia and rank attachments. The fact that you can actually buy them in XXXXL, supposedly ready-to-wear, is part of the problem.
I have several costumes I absolutely love but can't squeeze into any more. At one point I graduated from skinny Andorian to Klingon (when I grew my beard) and then to Tellarite. When I could play the Tellarite without the fatsuit
I started my diet.