Insoles often get less comfortable (not more) over time - the leather might soften as they 'break in' but, generally speaking, it's the *insoles* that will end up losing their 'bounce' over time. And they do the 'heavy lifting' on the support front...
So whether I return an item will depend on these factors of longevity & alterability (?) - sure, you can add heel grips/ toe caps/ arch supports to customise the fit of a shoe, but I often find these don't last for me (either they slide around or harden over time - a full insole works only if the shoe is deep enough to accommodate orthotics without my foot popping out). A cobbler may be able to stretch the shaft of a pair of boots a little or resole them, but they cannot change the fundamental shape of the shoe.
In other words, I tend to be strict with my shoe criteria - but that's likely because I only have (the space for) 13 pairs! Modern technology has made leaps & strides (pun intended :P) in comfort *straight* out of the box, so it *is* achievable - but it just has to be in the right brand, size & width for you.
I'm a little more lax with clothing if the fix is easy enough for my rudimentary sewing skills (shortening a hem & sleeves, swapping out buttons, taking in the waist, sewing a slit). I'd recommend doing a *thorough* test drive with multiple sizes before you commit though (doesn't Nordstrom offer 1 year returns anyway?) - you can see my recent weekend-long experiment with corduroy trousers in the forum, for example.