I would like to somehow set up a perspective that will contain all my tasks for the day, but only show them one at a time, such as the view option “first available” for projects.
I think there is a psychological benefit to only seeing one option for what to do next, so I don’t keep choosing the easiest options.
The only thing I can think to do is move all my tasks for the day to a project, then use the first available view option.
You might find Minus.app useful which helps people focus on one thing at a time. (https://minus.io)
Minus.app has a feature called Task Bar which reads from your OmniFocus and displays your topmost task on the desktop. It has a built-in timer, a pause button, completion celebration animations, and other attention-grabbing features.
You can also simply drag tasks from OmniFocus to Minus.app when you need additional concentration. When your OmniFocus task has a time estimate, the Minus Task Bar will read that too and start the timer automatically.
I am one of the creators of Minus. Here to help people focus.