Lots of good advice there.
OK, given that background, twilly, why not go up onto the Lewis tops? Lots of possibilities (always assuming decent weather).
An out-and-back if the weather window is short. A partial loop from Lewis Pass, through Brass Monkey biv, and out via either Rough Ck track or Lucretia & Nina huts.
Near 3-Tarns pass, there are a couple of tarns S and SE of Gloriana Peak that are worthwhile goals. Not simple topology, you'd need to concentrate on navigation. Or perhaps (from Lewis Pass) a traverse through Zampa to SH 1662, 1687, 1692, 1681 then drop down to Ada Pass Hut (+ side trip up to 3-Tarns?) and out via Cannibal Gorge Hut.
Hi twilly, I can certainly vouch for the trip that pageix referred to: https://tramper.nz/5343/waiau-clarence-pass-lake-tennyson-circuit/ as a challenging but slightly less committing alternative that still gets you to Blue Lake and Waiau Pass. We travelled in the reverse direction to that description and took 4 days. We walked from Blue lake hut to Caroline Creek in a day without any trouble at all, so I wouldn't be concerned about that.
Lake Tennyson Road, depending on the day of week, is pretty well travelled, whoever is driving up that road is highly likely to pick up a solo tramper.
Good luck and take care