It's not as much about "sharpness" but different way of displaying the image. Amstrad monitors use slot masks while Trinitrons aperture grille, and even that differs between consumer and PVM ones. You can check this
post/thread for more info on CTM monitors. The image from them does not look like the one on scanline-heavy PVMs, a consumer Trinitron is a bit closer perhaps. So if you want authenticity without actually getting a CTM, look out for a 14-21" consumer set, preferably non-Sony, since they use the same tech.
Or just get any smaller/medium & decent CRT and be happy, the *mask details are really not that relevant - as long as it's a tube, glass & phosphors, it's all good