I recently downloaded The Sims 3 from Steam and I have expansion packs such as "The Sims 3 Pets", even though I downloaded the base game from Steam can I still download The Sims 3 Pets expansion pack disc and it will work for the base game? Sorry if this question is confusing, all help appreciated!
This post https://gaming.stackexchange.com/a/55084/169790 says you can get your Steam version into EA Origins.
I recall registering physical Sims 3 disks on an Origin account, then getting digital access to them into the future.
Using this method, if you get all your Sims 3 games/expansions registered with EA, you'll be able to download digital versions of each of them and install.
Unfortunately not. To install the expansions on the Steam version, you will have to buy the DLC directly from Steam. Any disk expansion packs will not work unless you have a non-Steam, RETAIL edition of the game that came on a disk.