theretrofitsource is about the worst place to buy bulbs due to their high markup. Apparently, they also don't know what type of bulb 986/996 Litronics use.
The bulbs are
D2S, not D1S.
HID bulbs are not high-tech anymore, so paying more than $10 per set is just foolish. Any aftermarket HID projectors likely run $10 bulbs (mine do) and they are very bright.
https://m.ebay.com/itm/2X-35W-D2S-D2R-D2C-Xenon-Car-Replacement-HID-Factory-Headlight-Light-Lamp-Bulbs/272394738179?hash=item3f6bfdda03:m:mCWDteAlJ8j6a-a092JLyng
If you must pay more to feel more secure, you could spend 4x-25x more, but there is no need. Try the $10 set above and see for yourself. Worst case, you're out $10.
Stick with 5000k or below unless you like purply-blue lights.
https://m.ebay.com/itm/USA-German-Genuine-Philips-D2S-Xenon-Bulbs-Part-85122-Free-Ship/122108639372?hash=item1c6e3df88c:g:59wAAOSwT5tWKWP s