I am looking for the lightest setup possible for mostly dry summer time weather conditions.

So Ideas - Assuming air pad (8oz) & quilt (22oz).

1) Tarp/Fly with ground sheet.

2) Waterproof/weatherproof bivy only.

3) Tent only.

Considerations:
Tent and tarp setups provide (some) weather proofness but may be heavier that a bivy only.
Tents / tarps need tie downs and guy lines.
Bivy may be lighter but is open to the weather.
Bivy doesn't need any tie downs or guy lines.

Have you had experience using these types of setups with the most ultralight options?
Experiences?
Recommendations?

It seems that there is no perfect setup - they all have consequences and drawbacks.

At the moment I am inclined to just go full cowboy with a bivy only, but I don't want to get stuck with that if it's a bad idea.

Thoughts?
Thanks!