So, just get one with the shortest possible barrel, that way you can reach the trigger for sure.
Like for example 'Mossberg 590 Shockwave', would be good.
Careful though, if the Mossberg it doesn't comfortably fit in the mouth. Could be freaky to fire through your teeth. Remington 870 could be your friend
Might not look as friendly as the Mossberg, but that's what stickers are for. Some people even paint them beautifully
I have more thoughts
here
How to know whether the shotgun is short enough for me to reach the trigger while pointing? I know I can't measure it in the store or I will get sactioned real quick
You could look up the shotgun's specs online. You could also get a tape measure or tailor's measuring tape thingie, and at the store ask if you could measure it — because you'd like to see if such a small shotgun fits with your finicky gun mount