I have an Armor Ephro and I like it, kind of a mech with training wheels. There are certainly mods out there you can get that are tube style although it may or may not meet your expectations for wattage, but some of them are fairly high wattage. I mean, if you are doing it for the form factor alone.
Yes, you will need to research a fair amount and understand ohm's law and etc. if you want to use a mech. For me that was the easier part of the "hard part" TBH. I'm not sure your first mech should really be for out and about use because I'm fairly certain that if I did something dumb with a mech, it would be forgetting to make sure it was "in safe position" in my handbag and having it auto fire and whatnot. With mechs you need PRECISION (in your builds and calculations) and also consistency (in how you use it an care for it.) I did not buy a mech expecting it to be my ADV. That would probably be a disaster for me at some point and depending on your vaping style and battery you may need to carry more than one battery. IDK..
If you want to try a mech, try one. But don't expect it to be your ADV probably, at least not at first. I mean, I wouldn't.
If you don't like boxy shapes, you could get a slim one battery mod that may not be an EXACT tube but close enough to not split hairs over it, and you can always carry another battery if you need more wattage in a day than one battery can supply (in silicone case, away from anything like keys or coins or anything that could cause a short (battery cases CAN open when carried around, although it's rare.) Something like the Jaq B would possibly make a good choice, again depending on wattage needs, but it is well liked and has a slim form factor.
And, to explore all options there are always manpurses and satchels. I must say, the times I'm really glad to be female are when dudes are talking about their pockets and the pocket limitation.
I mean, get a mech if you want.... I just don't know that I would consider it the safest thing to use as an all day, carry around in pocket mod and etc.
Best of luck with whatever you decide.
Anna