i found a LOT of china/cheap 22mm downstems by just googling it a while ago. like 50+ of them and quite a lot of perc+length variety. there's only a couple on dhgate and they're not available in many sizes or twice the price of the other ones. most of them seemed to be sold at stateside retailers though which isn't ideal for some.
dunno where i saved the bookmarks to those but i have every 22mm downstem on dhgate in my favorites if anyones interested in that.
d020/matrix bubblers are the upper end of what i'd use with a ball vape without feeling like i'm losing too much flavor for smoothness. too diffused for less heavy hitting vapes. its the piece i use when i have a sore throat or to follow up a huge rip where my throat isn't 100% on my ball vape. its only really a good piece if you have a dropdown dry ac for it though, otherwise its a bit awkward and close to your face and would blowback probably. i had mine thrown in an order for free idk if i'd pay $40 for it.
what kind of vape are you using? the diffusion pump's my favorite ball vape piece by a long shot out of my collection. its designed to minimize diffusion and maximize cooling, and not really diffused, the vapor you get is more like the hit you get from a j hook than a water piece. it hasn't played nice with a bunch of other vapes i've had in the past though. only recommend it for ball vapes.
if i was buying glass for a vape right now and could only own one piece i'd probably buy
https://www.dhgate.com/product/2015-new-34-5cm-height-glass-bong-with-matrix/255741536.html if i was going for china, or i'd buy or
https://www.goorooglass.com/store/p101/HD_3_piece_bubbler.html or
https://texas-hot-glass.myshopify.com/products/sherlock-shredder if i wanted american. personally.