There are 3 gestures for posts. By default, you have upvote, reply, and mark as read.
Search gestures and change one of those actions to downvote. You can change the color so you know what's happening without needing to read the action being executed too.


Since you mentioned Ublock-Origin. I would recommend to disable 3rd party Iframes. That will mean tweets, youtube videos will not play by default but you can manually whitelist them at global or site local way if desired. Not loading Iframes by default should reduce the amount of trackers and potential malware that could be loaded from compromised sites.
You can see what level of blocking you can use according to your convenience here: https://github.com/gorhill/uBlock/wiki/Blocking-mode