I understand that cold storage wallets are the safest form of bitcoin wallets because they are completely independent from the Internet.
They are as safe as you make them be. A hot wallet on a completely clean, offline and secure PC is just as safe - but you need to really know what you're doing in order to keep the safety at a constant level. However, hardware wallets are more convenient as in you don't have to worry about
everything. They are supposedly safe even if you plug them into an infected PC. As long as you keep them up to date all the time, you should really be fine.
I also understand that a cold storage wallet may come in the form of a piece of paper, a hardware device, or simply a memorized seed phrase.
Depends on what you mean by "memorized seed phrase". If you're talking about a seed phrase that you try to remember using your own brain, that is a very big flaw. Imagine having an unfortunate accident that causes a memory loss. Or imagine having forgotten a word or two out of your seed - or the correct order. Using your own brain to remember a seed is a big risk.
I’d prefer using a hardware wallet because I’m more familiar with it and it's apparently the most durable of the three.
Again - as durable as the method of storage is. A paper wallet could be easily destroyed by heat/water. Hardware wallets are more resistant when it comes to the materials, but you still have to store your hardware wallet's seed somewhere. That could also be a paper. So keep this in mind - and a metal seed storage could come in handy in order to lower the chances of something going wrong.
Of course, I’m still going to use my web and desktop wallets but it would be nice to have a hardware wallet as early as now.
Using desktop wallets isn't a bad idea. But try to avoid custodial web wallets. I mean, try to avoid web wallets at all. You could use your hardware wallet with compatible web wallets - that's fine, because you'd still store your coins on the hardware. But avoid Blockchain wallet, Coinomi and any other custodial/closed-source wallet. There's Electrum - it does an amazing job when it comes to being both fast and convenient and has a lot of functions as well.
Also, try to use your hot wallet only for short term txs. If you need to make a payment, use that hot wallet temporarily for it. Afterwards, move all your funds back to the cold storage.
Someone told me that it’s best to buy a hardware wallet directly from a manufacturer to avoid getting a tampered product. Is that true? How risky can buying from a reseller be?
It's usually recommended not to purchase it from a reseller. Think about it - is it worth paying $10 less to later find out your device has been tampered with and your funds just poof as soon as you send them to your HW?
There could even be fake wallets (IIRC, there was a fake Trezor selling around at one point) you might purchase unknowingly. Therefore, the best thing you can do is just get it from the original source or authorised sellers (you find the authorized ones on official hardware wallet websites).
Can you recommend a good brand or manufacturer?
Trezor and Ledger are the most widely used and known. I own both of them - it really depends on what coins you want to store and what functions you want the HWs to have. Check out both websites and their products, compare them and see which one you like more.