I like small as well, and I like tough to break too.
Here's my solution.... The size of fat ball point pen or a marker pen.
It's an ego-t battery with a collar on it and a vision mini vivi nova mounted on it. I believe it's 600 mah and lasts me 6-8 hours on a charge. I charge 2 batteries every night, I put one on the nova in the morning and just bring a spare batt and a 10ml bottle with me if I'm going to be out and about for 12 hours or so.
I also swapped out the clear tank for an aluminum tank for even more durability as the threads on the plastic tanks must be handled with care and strip out rather easily. My main reason was that I do not carry around bags, just as I wear zero jewelry and not even a watch, and I got tired of breaking ecigs and such in rough usage as I do a lot of outside work, mechanical work, carpentry etc. and I need small tough and convenient. I don't like carrying big stuff around, nor do I like carrying a charger or several batteries, I can live with carrying one in my pocket (turned off) and the whole rig in a pocket as well.
The vivi mini nova holds 2.5ml and is very easy to disassemble and clean, very easy to replace atomizer heads in it at a couple bucks per new head, heads are available in several resistances, and with the aluminum tanks its very unbreakable and I have zero worries about what juices might break down a plastic tank. They are also one of the easiest clearo/tanks to manually make your own diy wicks and coils for as well which I do.
The whole rig is about 5 and half inches long and just over a half inch in diameter, and just drops into my pocket in my jeans and won't break even if I put it in my back pocket and sit on it, or drop it and step on it. Easy to stealth vape as well, and it's never very conspicuous. I have had zero leaking issues, though you do need a rather small tipped bottle or it's easy to get juice in the center of the atomizer when filling that you simply have to blow out before screwing the batt on.
Downside is that you can't see how much juice is inside with the aluminum tank, you have to learn to judge when you should be getting low..
Some have wicking issues with the novas, and dip the tip down and such to keep wicks wet. I find this is only an issue if you don't vape with it level and horizontal, I always vape with it level and horizontal and have no such issues.
Anyway, there are many options for a decent small setup that is convenient and easy to use, clean and rebuild, this is just the one I have settled on, at least for now, for the best size, durability and function I could get in such a small package.