I keep talking about the Dead Foot Arms Modified Cycling System, which allows a much shorter buffer that facilitated adding a fold stock/brace that allows for shooting the gun while folded. It's expensive, but it's the only solution if you want to use a direct impingement AR that can be shot with the stock/brace folded.
Otherwise, you could go with the Brownells BRN180 uppers--but they're twice the price of the Dead Foot Arms folding stock setup.
Dead Foot Arms: https://deadfootarms.com/
Brownells: https://www.brownells.com/.aspx/bapid=700/ClientPage/brownells-brn-180