Vertically Stacked Dimensions Mod 1.12.2 has shared a more lightweight solution to extending the world vertically. Meanwhile, it only makes the game become different a bit.

About Vertically Stacked Dimensions
It extends Minecraft in a vertical way by stacking multiple dimensions on top of each other. Additionally, it combines those dimensions with portals. So, you can move to the next space layer if you hit a vertical border.
Main features
They are also abilities that the mod allows you to do.
Modify the ore generation for individual dimensions (also supports non-even distribution models)
Add custom layers of arbitrary blocks (and optional bedrock as the out-fading effect)
Take the place of some blocks at certain heights while generating the world
Create Nether-like terrain within arbitrary dimensions at selectable heights by launching customizable blocks
And more
Until now, the author doesn’t supply additional dimensions. In other words, the release will base on dimensions that other mods supplement.
List of mods adding those dimensions
Just Enough Dimensions
Dimensional Control
Open Terrain Generator
OTG: Skylands
The Beneath
Cavern
No Nether Portals
Configuration
You’re able to generate another world by default. The present edition will only drop the Overworld on top of the Nether dimension. There are two options to change that.
Utilize the Stacked Dimensions button
Edit the configuration file
Remember that the config file provides many more choices and features than the in-game GUI.
Pick Vertically Stacked Dimensions mod if you’d like to extend the realm in Minecraft! It requires Minecraft Forge to operate.
Requires:
Screenshots