Tree-climbing gear for my gravel bike?

[BumbleBeeDave]

On my Lynskey Pro GR I’m currently running a Shimano GRX 31-48 crank on the front with the rest of the group eight-year old Ultegra 6800 11-speed with 11-36 on the back. I’m a spinner, and this 31-36 combo is just not low enough for me.

The Ultegra needs to be replaced anyway, as it's eight years old and has seen a lot of miles, plus my left brake lever (hydraulic) is not working really well any more. I want new stuff.

I’m planning to replace the rest of the Ultegra with mechanical GRX and keep the current crankset, if possible, given that I just bought it a few months ago. But the lowest I can get with the two ring GRX group is that same 31-36 combo.

Is anyone here running a mullet setup with a bigger cog in the back for lower gearing? If so, what parts are you using and how reliably does this setup work? I’d like to run at least a 42 cog in the back and possibly higher.

Also, I know a one ring setup would let me run a 40 front and something ridiculously big in the back for lower gearing. But what are the disadvantages–if any–of only having 11 active gears instead of the 22 with the two-ring setup? Too big a jump between gears? If you ride this setup has that been a problem for you?

Any comments/advice appreciated! I don’t want to get this all bought and built up and find it doesn’t do what I need/want.

BBD