Please take my comments with an extra grain of salt, as I'm rather heavy compared to OP.
I share only because earlier in my foiling path I though the best material for ULW was a Peak (because it is so difficult to make it fall) and a large fat foil with lots of low speed lift.
In time I reversed my view (and I began to agree with those offering differing opinions at the time): now when I decide want to go really light wind, nothing beats a
big kite producing lots of apparent, and a very glidey foil with as little drag as possible (and no real need for ultra low speed lift).
The issue is this: in very light winds, it is not easy to get apparent to kick in
and and have it strong enough to maintain direction (so transverse is easy, upwind is very tough).
And then, as soon as you need to change direction, either you're very good at roll tacking and do it race style at speed (not my case...) or you jibe, and that is both boring (as you lose speed) and thrilling (as you can slack lines, or crash the kite with the loop, or end up stopping because of foil drag and fall down from foil having the kite fall down too without apparent wind).
So, as glidey a foil I can manage (The Fluid L-s for me with Fluid 40 by GONG, soon with the new less draggy stabilizer), and as big a kite I can hold, because in ULW I'd rather need to trim when apparent wind kicks in than enduring the pain of constant kite zipping around to generate apparent and trying not to stall. Big kites truly kick apparent in and remain nice (in straight lines) in ultra light winds. Smaller kites may get you on foil, but riding will be more work than fun, and that is why I stopped to use my 10m Maverick in 7/8 knots.
Glidey foils with as little dragsas possible mean accelerating more (thus more apparent) and losing less speed during manouvers mean much higher leeway, and more relax/fun.
So for me, 6 knots (but 7 is better: real 6 knots is really mild wind) is (now) 17m Strutless by GONG, which gets overpowered quickly is true, but allows my 110Kg to jump on the foil and out of jibes easily, and also allows me proper upwind. You go fast, you can try jumps, and provided you are decisive enough with steering to avoit it hitting the water with kiteloops you'll never stop even in lulls.
Very nice for this was my Ultra 17m too.
Board size is basically not mattering even at my weight: newer higher a/r foils respond greatly to pumping, so looping the big kite around and pushing with the legs will eventually get me on foil even on my 108cm board.
Even if I feel the lift for just a fraction of a second, I only need to get vertical or so, and then pumping while moving the kite I will eventually get the foil to gain speed and lift me.
I see very light dudes around here in lighter winds I'd dare try making it with ridiculous pocket boards: besides ability, weight is an essential part of the equation. And they use a 11m kite at 50Kg with quite a few years of ULW scraping.
Last, but not least: my last outing (6-8 knots) on the 17m was with only 20m cables.
Sure I lost lots of useable window, but the faster kite allowed me to chain large loop after large loop even on the 17m to get on foil.
So, my recommendation to OP would be to jump directly to a slightly bigger kite.
At 70Kg if I remember correctly there's no need for a 17.
But on of our good riders goes out in 6 knots on a Ultra 14 at 72Kgs, and holds it until 12 knots or so.
And at 7 knots he has lots of fun already.
P.S.
The Contra 1s ('21 and '22) I see flown all the time from by my riding buddy, and he loves it. I can vouch for its low wind pull, but I never gelled with it.
My feeling is other kites have proved better suited for ultralight winds (in my hands at least), and also that Cabrinha fell prey of the nouvell vague dictating that "anything over 11m is not good for foiling".
I dissent strongly.
Lots of people foil with 14/17 pumps and 15->21m foil kites in very marginal winds.
11m is just the largest size one can charge ridiculous amounts of money for a kite behaving "acceptably" in the head of a user: larger kites are indeed sluggish, and the user really needs have clear that it's those limits (i.e. speed...) that make these kties suitable for scraping the last knot.
My 2c, of course.
P.P.S.
Or a 12m or 14m Aluula might do the trick... but those are almost 3k
, and those are kites that get the most out of apparent rather than offering easy "instant pull" like the contra.
The Gong strutless is a known name for this. The Maverick nerio (I own the 13m, but should have gone 15 in retrospective at my weight) is a very, but very nice kite for these conditions, as it is fast and it gets lots of power with speed.