You sound like you're fairly new to concealed carry. Maybe I'm wrong but the questions you're asking and the assumptions that you seem to be under do point that way.
I've been carrying every day, virtually everywhere, for the last 14 years. I've learned a thing or two in that time...…..
You're VP9 will absolutely disappear under a properly sized garment in an IWB holster as long as you select an appropriate holster and appropriate belt. Polos tend to be a bit more clingy than square-cut button down shirts worn untucked. With a regular (not fitted) untucked button down shirt I can conceal a pistol the size of a VP9 in a pancake belt holster with ease. Leather pancake holster work better than the kydex versions because leather molds to your body and will pull the pistol in tight (assuming you have a proper belt).
DO NOT, I repeat, DO NOT carry a pistol on the small of your back. First of all, it's the slowest position to draw from. Second of all, it's going to suck when sitting down. Third, if you have to go hands on with someone and you end up on your back, you will lose access to your pistol. Fourth, if you fall on your back or get taken down hard that pistol is going to hurt you.
AIWB (appendix inside the waistband, basically between your centerline and your 1 o'clock if RH) is the fastest draw and very concealing if done well, but I'm told it takes quite a bit of trial and error to get right. I have a thread on that here since I'm considering it.
For someone like you I strongly recommend you stick to strong side carry for now and experiment with AIWB as you get more comfortable.
I have no idea of what kind of support gear you have so I'm going to make the recommendations based on my own experience. YMMV.
Since you almost never conceal with an open-front garment, you don't need a dressy belt. You need an effective belt. I haven't found a more effective belt than the
Ares Aegis. It's comfortable, infinitely adjustable (very important) and extremely stiff where it counts (the most important aspect).
Get yourself a high quality pair of leather holsters. If you read the internet you'll get the impression that no one uses leather any more. Not so. Leather is king over kydex when it comes to both IWB comfort and OWB concealability. Kydex lasts forever and is cheaper, which is why it's so popular.
I have had leather holsters from tons of people. Of those I've used, TT Gunleather and Nelson Holsters are my favorites. From those two brands, here are my top pics.
IWB:
The Reinforced Inside-the-Waistband (IWB) holster has been meticulously engineered for discreet carry, designed to be comfortably situated within the waistband with purpose-built loops for secure attachment to your belt. Tailored for wear between the 3:30 and 4:30 positions, this model features...
www.ttgunleather.com
OWB
This model is a pancake-style holster with a 14-degree cant, typically intended for wear between the 3:30 and 4:30 positions. Its moderate ride height and opposing belt slots ensure a close and secure fit against the body, enhancing both comfort and concealment. This holster is available with...
www.ttgunleather.com