I don't know which spokes Rohloff supplies these days, but I have a bike with wheels built a dozen or so years ago with Sapim Strong spokes with the special Rohloff elbow bend, and they're still drum tight. I were you, I'd take the spokes Rohloff offers and build the wheel to Rohloff's recommendations (actually, if I were you, and these were normal times, I'd get SJS to build the wheel) and with Sapim's matching Polyax nipples to tune out any remaining angular stress.
The Sapim Strong are butt-ugly spokes, and I'm not making a pun, but with the Rohloff bend they work like a charm. Pictures of spokes, nipples and end result at:
http://thorncyclesforum.co.uk/index.php?topic=10979.msg79497#msg79497
Good luck with your wheels.
PS Unless you go for an expensive "professional" nipple spanner, nipple spanners usually have three slots on them, and the chances are one will fit. Or you could just go for the most comfortable one, the red Spokey being the right size, 3.25mm, see
https://www.sjscycles.co.uk/tools/spokey-red-for-euro-us-spokes/ (https://www.sjscycles.co.uk/tools/spokey-red-for-euro-us-spokes/)
(https://www.sjscycles.co.uk/images/products/medium/12838.jpg)