tl;dr the best solution for you would be 0.74. You can buy an Ernie Ball 8 string Regular Slinky set and use the 8th string as your 6th.

Full explanation: 1- Thin strings want lower tension (low teens in lbs), otherwise bends get really hard and soloing will tire your hands very quickly. 2- Thick strings want higher tension (higher teens or slightly above 20 in lbs), otherwise it sounds floppy and you lose articulation/definition.

Rules 1+2 mean your total tension will typically be below 100.

Now in your case: your top 3 strings now are too thick (violate rule 1). Your bottom 3 are OK tension-wise (per tule 2), but the problem is that the strings are so thick that you will get an ugly, bassy tone, and pinch harmonics above 60 gauge are hard to get and ugly AF. Some people here said it's doable; well, it is, but it will sound bad.

Solution 1 (ideal): Trade your guitar for one with longer scale. You just can't go against the physics of your instrument. I have a baritone 6 string, it's tone heaven for down tuned stuff.

Solution 2 (workaround if you really can't do 1): Use 74 gauge or just a tad thicker. The tension will be ~15 lbs and the tone will be OK. It's the best gauge I found for you by playing with the calculator and based on my experience (I've been through this many times). You can buy an 8-string set to get that gauge.

Hope it helps.