Recommendations for carry on case with separate laptop compartment

So I have been looking around for 20 inch cases and always come across able or similar cases with a separate compartment for a laptop, they are terrible sized, cant fit a 16 inch at all, despite having enough space in the bag, their pockets and areas for storage for laptops is terrible.

The wishlist is pretty simple. I just want a hard shell bag that has a separate compartment for a decent size 16 inch laptop like a ThinkPad etc. I want to be able to lock it separately with tsa lock. The rest of the case can be the bog standard with tsa lock etc, no zips, however I do know it restricts the ability to expand because of lack of zips, but I am ok with that as long as I can fit a laptop in there.

Any suggestions?