In recent years I mainly use a bivvy and a tarp shelter, and often dispense with a groundsheet.

I think bivvys are highly over-rated as a complete shelter, and greatly under-rated as a "sleeping-bag accessory." Offers various advantages that I much appreciate.

Mine is OR bivvy with a waterproof bottom and water-resistant top. Don't need a waterproof top, and has relatively good breathability and somewhat economical price.

It weighs about one pound, so it's not really what you're looking for, and regardless, it's been discontinued for several years. Don't know what will replace it.

A super-ultralight might be too delicate for my taste. I sortta like the "iron-clad" notion when sleeping on a pile of muddy gravel...but not too sure. OR sold me, somehow, on their coated fabric used for the floor. Don't know that it's really all that great, but it seems somewhat heavy duty.

I do like the OR zipper configuration pretty well: an arch at end of bag, rather than across the face. One is probably not better than the other.

I wish it had a somewhat wider girth.

I think it compresses my winter sleeping bag, and also if it were wider, it would be easier to store minor bits of stuff, etc., inside while in use. Obviously this would add some weight, but otherwise there would be little downside.

I find it surprising that very few manufacturers offer more than one girth size.

This isn't a critical consideration, but just a pet observation of mine.

As for tarps, personally I prefer a "shaped" tarp shelter with integral door, which tend to be heavier than the simple rectangle, or designs with open ends.

I have a SilShelter that I've used a fair bit, but have mainly moved to larger designs after getting cooped up in the thing for a while.