Based on your (thanks, detailed!) comments, my guess is that adding an inner net tent to your Golite poncho tarp wouldn't satisfy you. I have a Golite poncho, and indeed, my inclination in terms of using this as my shelter is to take it only on trips where I don't expect extended bouts of bad (wet) weather. It can work, but it's tight, site selection is important, and contrary winds/weather can cause issues anyway. A net tent that would work with it would not likely allow you to sit upright comfortably.

A single-walled tent is a common solution to the weight issue, but it's not clear from what you wrote whether you would find that acceptable. The usual places to look for such a shelter are tarptent.com, sixmoondesigns.com and likely others.

You might consider lightheartgear.com, I've been very happy with their solo tent. sixmoondesigns.com now sells one of very similar design to theirs; I've seen it, but have no experience with it. I think that this sort of hybrid single/double wall tent design is really excellent for those that use two trekking poles.