i've been using the blank spaces launcher for this. it has its flaws for sure, but the feature most useful for the scenario you describe is the "Lock Distractions" feature. In order to use safari, you have to go through a "mindfulness" exercise, and then you can unlock safari for a small amount of time (1 minute, 5 minutes, up to 20). I find this is just enough to keep me out of random wikipedia pages all day, but still allows me to pull up a webpage when i need to do some very specific task (like unsubscribe from an email list).