Use the HST and JWST pages for space wallpaper sources[1][2]. Make sure to check only the 'observation' checkbox; this filters out all the infographics, 'artist's impressions', simulations, etc.
I suggest downloading the TIFF, opening this in some photo post-processing program (Lightroom, Darktable, RawTherapee, etc), and applying mild tone and colour adjustments, and then cropping to the exact resolution of your display.
I get much better results this way.
