Mixing Ultegra crankset with MTB shifting

My gearing is too low. The best solution is to convert the front crankset to a road style which offers a 53T ring.

Currently I have a Shimano SLX Hollowtech II crankset (44-32-22) + SLX FD + Deore LX 3spd flatbar shifter.

I'd like to replace the crankset with an Ultegra. Probably a 53-36. Another option might be a 3-ring Ultegra if I can find one.

Anyway, what I want to know is what i can/must do with the SLX FD and my Deore LX shifters.

Can the SLX FD properly shift on an Ultegra crankset (whether it's 2 or 3 rings)? If not, and I have to put a real road front derailleur on, will the Deore LX shifters be able to drive that derailleur? Or do I have to find some Road flat-bar shifters (uh oh).

If I have to use a road FD, the ultegra will be bottom-pull, when my bike is set up for top pull. I think I can solve that with the aid of a Speen "umlenker" adaptor. Has anyone used these? It sounds cleaner and easier than a pulley system.

First, if a standard Ultegra(not compact with smaller bolt circle diameter), smallest small ring is 38t.

Next, you can find a front derailleur that is compatible with the LH shifter, a mountain/MTB shifter it must be(road FD are not compatible with MTB shifters) but try to find an older one that was made for bigger chainrings like 46/36/24. It will match the curve of the crank better.

Install and adjust. Shifting won't be ideal but with a little shifting finesse, it'll work on a double crank.

Not to over-simplify the situation, but have you considered installing a 48t chainring on your current crankset?

Shimano makes both a steel & alloy 48t chainring.

A 48t chainring WITH an 11t smallest cog is a higher gear than most REAL people (non-racers) need in most riding situations ... even for going downhill on a mountain road.

N.B. If your frame has 135mm rear dropout spacing then you CANNOT install a standard double crankset which has a 150mm Q-factor on your frame because the chainstays & the chainrings will compete for the same space + the crankarms MAY also not have clearance. This means a so-called "Compact" crankset is out of the question ... and, you will need to use a TRIPLE crankset whose Q-factor is ~10mm wider.

FWIW. I have used an 8-speed XT front derailleur (737) with a 52t chainring & I presume it could be used with a 53t chairing, too.

BTW. The "common" solution for using a ROAD front derailleur on a frame which has top pull routing is to use a "pulley" wheel.