Upgrade without paying for base game?

Hello, I recently decided to give GW2 another try, after not playing since a short time after its release (probably put in 20-30 hours over the course of a few weeks), and obviously I noticed that there are two expansions now. While I am not certain whether I will end up getting back into the game and buy them, I am at least considering it at this point. I see that buying the expansions grants access to the base game, but I am wondering if there is a way to upgrade without paying for the base access as well.

Please let me know if I am missing the option somewhere!

The base game is included for free in every expansion. There is no way to get any expansion without also getting the base game. You can use the expansion code to upgrade an existing account or to create a new one.

Do I get an extra game's worth of character slots or anything like that at least?

No, you get nothing extra. People who pre-ordered HoT and already owned an account at that time got 1 character slot. That's it.

Understood, thanks.

https://help.guildwars2.com/hc/en-us/articles/230165307-Guild-Wars-2-Account-Types-Free-Core-HoT-PoF

Here you can find more informations about the different type of account.

Very helpful, thanks. I didn't realize that there was a free playable account now, that explains the reasoning for the answer to my second question.