Fairly wide angle advice

Hello,
I'm back into using my camera after a few years off, i just acquired a 16-85mm for my holidays, unfortunately i was dumb enough to buy a "cheap" Hama CPL which i left on the whole time (lazy?!), my photos are mostly soft. I will try next week on a trip to Amsterdam, using a new expensive CPL (K&F Nano X), and also without filter this time.
After that trip i had my son's birthday and took out my 35mm and 50mm, i am very impressed with the results of those prime lenses, and i also love the size and weight. Would love to get something similar but wider, ideally around the 20mm.
I have a 24mm old manual Sigma 2.8 which i find very good, however with kids moving i find it difficult to have things in focus, i realized there is a newer (still 20+ years old) autofocus, which i can acquire for about 150 euros it seems.
I also see there are some older Pentax 20 and 24mm, very hard to find it seems though (and pricier). I wonder if I should stick to the Sigma. I also the Pentax 21mm which is now cheaper but the reviews aren't convincing, I had a HD 15mm a decade ago, and though the reviews claim to be amazing, it was way too soft for me to be usable unfortunately.
Any lens I may be missing? i don't mind spending a bit more if needed, though i find new lenses prices above 1K to be a bit excessive for my rare shooting..
I also saw the 11-18mm, wider, shinier, but much bigger too, which i would consider to replace my 10-20mm sigma, but the price is also a big turn off.
I shoot on a KP so it's APS-C cropped sensor.

Pentax 12-24 is reasonably priced and good.

thanks, i had it awhile ago, i decided to keep the Sigma 10-20mm, i can't remember exactly why. But (aside from my last comment about the 11-18mm which i guess makes this post confusing), i am leaning towards a prime-light-super sharp lens.

I have a 24mm f1.8 Sigma. Image quality is ok but it is large and an older design. Perhaps the 18-35mm f1.8 might be suitable.

I would suggest the SMC Pentax-DA 12-24mm f/4 lens. It's no lomger in production but you might find one second hand. It's a great lens.

I didn't know it was out of production. Will hang on to my copy - very nice lens.

Another vote for the sigma 24 F1. 8
Works well on the k5iis

thanks a lot, i did not realize there was a 1.8 version of the 24mm Sigma, however it looks too big/bulky, unless someone can say the image quality is much better than on zoom lens, i dont think it makes sense for me. (as in i would like to have a super small lens to carry around, same size as the 35 or 50mm)

One of the Chinese makes may have a suitable lens but most options for Pentax are good zooms (12-24 or 18-35) or larger older designs like the Sigma. You should be able to find the 24/2.8 AF Sigma for less than €150. This would be a good option - compact, good image quality.

Thanks yes I’ll keep looking, doesn’t seem to me many options at the moment but that can change.

I've used the 21mm HD Ltd lens, my copy seems very sharp, also it's light and tiny on the camera body. Here's a example of an image using it:

link

Looks good to me.

thanks for your advice, i've just ordered a 21mm f3.2 (older version), hopefully i will receive it on time for my upcoming trip to Amsterdam on Thursday.
I think i will also buy a Pentax * 24mm f2 from Japan at some point, i haven't ordered anything from them yet so i'm a bit nervous, prices seem fairly good (around 250 euros to which i believe i need to add 50 euros for VAT so 300).
I might also get a 20-40mm.
It's been awhile since i bought a few lenses to try out.

The 24-50mm SMC-F zoom might also be an option. Not super fast aperture but a good performer and good value.

The 21mm f/3.2 is a good lens but make sure to check that it focuses properly at infinity - mine didn't always but was very good indeed at shorter focus distances.

I'd recommend staying away from pre-digital-era Sigmas in general as the quality can be very hit-and-miss. The newer 10-20mm f/3.5 though, is excellent.

For a focal length around 20mm I would recommend the 20-40mm Limited zoom, which is a superb lens when it focuses properly (check for front and back focus at all focal lengths). This and the 16-85mm are the best Pentax zooms I've used and are better than many primes.

Bad quality filters can soften images and bad quality polarisers can rob them of contrast and add colour casts too. Always check image quality with a new filter before using it for proper photos.