I'm plugged 20-ish hours a day every day (except when I'm on my period) and sleep plugged every night. I use either the Squarepeg Egg XL (8.5" max circ) or XXL (9.3" max circ) depending on what's comfortable at the moment, and I can say that there's nothing painful or unpleasant about long-term wear of plugs of that size. I'm planning to add the Topped 100 (10" max circ) and slowly phase off the XL. I realize in the scheme of things these aren't huge, but I think they're larger than most people (probably not people on this board, lol) would think of as comfortable.
Use silicone lube overnight (yes you can use silicone lube with these particular plugs even though they're silicone), choose a soft plug (Topped is a good choice), and make sure you have enough fiber in your diet to keep things clean. I don't do enemas or douches and 99% of the time my plugs come out clean because I take fiber and my body has gotten used to being plugged.
Fyi about relubing throughout the day, while I am certainly not suggesting that lube isn't important, I think it the talk of constantly relubing is exaggeration or people who aren't as familiar with semipermanent plug usage. I use water-based lube during the day and never have to take my plug out to relube JUST to relube. Why do I take my plug out? To pee. When you get up to larger sizes it becomes difficult to pee while plugged because of internal pressure. That's when you relube if necessary or, as in my case, reactivate the lube with a bit of water and slip the plug back in. Honestly, plugging becomea routine for you you're going to find that too much lube is actually a problem for retention. You don't want a dry plug, but you do want something that'll nestle in and grip a bit.
Anyway, best of luck. Permanent 24/7 is my biggest fantasy too, and while that may not be practical I'm happy with what I am able to achieve.