Composite block from multiple other blocks + layout
Use blockgroup. Add block_class if needed.

When creating the block groups, make sure that the machine name does not clash with existing theme region machine names! (from any theme, ideally)

After you created a block group, it will show up in two ways in the blocks UI:


As a new theme region (if you avoided the name clash)
As a block that can be placed.


Block class allows to add classes (e.g. bootstrap grid classes) to each block and block group.

This is not 100% what you would get with a layout, but it is getting close, and will be sufficient in many cases.