Reddit mentions of Spigen Liquid Air Armor Designed for Samsung Galaxy S9 Case (2018) - Matte Black

This one meets all your requirements plus is compatible with a tempered glass screen protector

Samsung Galaxy S9 Case, Spigen® [Liquid Air] Galaxy S9 Case with Light but Durable Flexible Protection with Geometric Pattern for Samsung Galaxy S9 (2018) - Matte Black - 592CS22833 https://www.amazon.co.uk/dp/B0789T8P88/ref=cm_sw_r_cp_apa_hD9NBbER89Z91

What i did, since they are basically the same, was look at the best cases for the S8 and S8+. Manufactorers are not going to reinvent the wheel when they only need to update the camera cutout.

I ended up going with this case if you need something to start with.

It was well rated for the S8. It was even higher rated for the iPhone versions.

I prefer this one:

Spigen Liquid Air Armor Designed for Samsung Galaxy S9 Case (2018) - Matte Black https://www.amazon.com/dp/B0789T8P88/ref=cm_sw_r_cp_apa_i_4X3HDb1A8Y5RS

Much less beefy and bulky. Fits on the hand well and does not add much weight or uncomfortable feel.

Spigen Neo Hybrid Designed for Samsung Galaxy S9 Plus Case (2018) - Gunmetal https://www.amazon.com/dp/B0789S2LZH/ref=cm_sw_r_cp_apa_i_EY3HDbXVZ92HX

This is a good alternative. But its does feel less ergonomic than the Liquid.

I have bought a Spigen and Tech21 and have decided to keep the Spigen, it just feels a lot better! In relation to the screen protector, I bought the below and is great! No bubbles and great to put on (comes with an accessory) Case https://www.amazon.co.uk/gp/product/B0789T8P88/ref=oh_aui_detailpage_o04_s01?ie=UTF8&psc=1

Screen protector https://www.amazon.co.uk/gp/product/B079ZCKT3Z/ref=oh_aui_detailpage_o04_s02?ie=UTF8&psc=1

Spigen Liquid Air or Thin Fit. I have both, among other cases, and use the liquid air as my daily-use case. The thin fit is hands down one of the thinnest/lowest-profile cases you can get for your S9/+ that's still high-quality, and will keep the screen from touching any flat surface it's on (granted, it's only about a milimetre or less above the surface, and the case doesn't protect the side buttons). I'd go for the liquid air personally - it's a bit thicker while still being lower profile than most other cases, and will give a fair degree more protection than the thin fit.

My girl and I are huge fans of Spiggen's "liquid air" cases for both of our S9s, and our S8s last year. They're slim enough, there's enough space between the side bezels and case for a screen protector to NOT get f***ed up from rubbing against the case, they look fairly minimalist, and they're inexpensive to boot. Because the loop around the top and bottom bezel is raised, it's saved my ass as I've dropped both my S9 and S8 face first on multiple occasions without a scratch or crack... Like, pretty nasty drops.
In case you're interested, here's the link on Amazon:
Spigen Liquid Air Armor Galaxy S9 Case with Light but Durable Flexible Protection with Geometric Pattern for Samsung Galaxy S9 (2018) - Matte Black https://www.amazon.com/dp/B0789T8P88/ref=cm_sw_r_cp_apa_i_5E51BbQEQY4AG

I've heard good things about the Whitestones or whatever they're called, but that's a lot of money for something you may mess up installing (people get nervous, or don't do it on 100% flat space, or they rush it), so I I've been apprehensive about purchasing them, and instead just get flexible film screen protectors and swap them out every few months. This is worked well for us, though it does feel a little rubbery and you know obviously it's not 100% clear like the glass protectors are. Delta Sheild makes these (I'm sure they're just about the same as everybody else that sells the thin film protectors that "self-heal", but they have excellent customer service and lifetime warranty for literally anything. You screw up the installation, or just get scratched up over the course of months, whatever... No matter the reason, they replace it for free of charge with no questions asked, and they always send you 2 per pack.
Galaxy S9 Screen Protector [2-Pack], IQ Shield LiQuidSkin Bubble-Free [Case-Friendly] Screen Protector for Galaxy S9 HD Clear Film https://www.amazon.com/dp/B0754KFP27/ref=cm_sw_r_cp_apa_i_cM51Bb64M4MXY

This is what I picked up over the holidays and have been loving it. While not the thinnest of cases it works for my daily driver. Not sure how much stock I put in their corner protection tech but it's slim, has a nice texture on the back, has raised up top/bottom lips so you can flip your phone over, and still get full access to the phones edges.
https://www.amazon.com/Spigen-Durable-Flexible-Protection-Geometric/dp/B0789T8P88?ref_=bl_dp_s_web_5299909011

using that one https://www.amazon.it/Spigen-Liquid-Air-592CS22833-protettiva/dp/B0789T8P88 but i don't like it, phone it's well protected btw, waiting for some discount to get some thin cover like that https://buypeel.com/products/super-thin-galaxy-s9-s9-plus-case