Pentax is amazing when it comes to these super compact Limited lenses. DA 21mm, DA 40mm, DA 70mm... you can pack three high quality primes with amazing rendering into a small small bag, and you are set for
most situations. Add a fast 50mm and maybe something a little wider (15mm) and you are
set! It is too bad the DA 21mm is APSC and there is no direct equivalent for FF. I think Pentax will release another wide angle prime after the announced 50mm and 85mm. Something between 20 and 28mm, FF compatible, but we don't know
when.
I don't want to keep repeating myself, but my vote goes to a good old 28mm (F, FA) and DA 40mm (can get the HD limited if you want to splurge, or just the XS if you want to go budget). Or an older manual focus 28mm (I recommend at least A series, so you have auto aperture). Or a
Voigtlander - fairly compact, good quality rendering, people love these, but they are rare and hard to find.
The mentioned Sigma lenses are all fairly big, and the 30mm ones have some problems. The older one has triangular bokeh highlights, many of the new Sigma lenses have AF problems.. and they are all pretty big. Sigma is no longer the super cheap competitor, now their lenses aren't cheap as chips. And the final straw - OP wants something that
renders like the DA 21mm. Sigma is making reputation for sharp lenses, but not for lenses with amazing colours and contrasts. I've seen some posts complaining about the general Sigma 'look' and expressing a preference for Pentax.
To each their own! Hope OP finds what they need