Plenty of mods have tried to put two slabs inside one block. One major problem you encounter is that using too many in one space causes lag. Block Slabs doesn't try to use entities or containers or do anything fancy, it simply adds over 1000 variants of blocks that are half one slab and half another. Initial load will be heavier than its counterparts but overall performance should be better.
Block Slabs also paths the default minecraft textures so it is friendly with nearly every resourcepack available.
See below it being used with Conquest Reforged
Block Slabs is completely survival friendly with crafting recipes for each of the blocks being to simply combine a log or brick above or below a plank or log. The creative menu is divided into four tabs for easy searching
Its currently only available in forge 1.19 but I do have plans to release it across multiple versions
If you would like to support this or any of the other things that I am working on Patreon is an amazing way to say thank you.
Come say hi, ask questions or make suggestions for the mod
I stream over on twitch
Lore heavy timelapse builds