How can I get all Destiny 2 expansions?

I pre-ordered the Destiny 2: Shadowkeep game for $35 and I got the base Destiny 2 game with the year 1 expansion packs -- Warmind and Curse of Osiris. I will be getting the Shadowkeep DLC later on when it comes out and I will get its expansion pass later on when it actually arrives.

My question is: Can I buy the Forsaken DLC with its 2 expansions now? I can't see it on the store at all, only the $100 edition which also includes the base game. Do I have to buy this edition to get Forsaken? I don't want to have to pay for another copy of the base game.

This has been covered off in this weeks (6/13/2019) This Week At Bungie.

Specifically,

Forsaken and New Light
Q: Will Destiny 2: New Light be its own separate game/file?
A: No. All Destiny 2 players will be automatically converted to New Light and will maintain all of their prior purchases and entitlements.

Q: What Forsaken and Forsaken Annual Pass content will be included in New Light?
A: Forsaken content available in Destiny 2: New Light includes: Free roam on all destinations, Strikes playlists, Crucible playlists, Gambit and Gambit Prime playlists, Select Annual Pass content

Q: What Forsaken and Forsaken Annual Pass content will NOT be included in New Light?
A: Forsaken content available only with purchase includes: The Forsaken campaign, Year 2 raids, and dungeons Exotic quests

So you'll only need to purchase Forsaken if you'd like to play the Forsaken campaign, dungeons and acquire Forsaken exotic items.