https://www.macys.com/shop/womens-clothing/womens-pants/Brand/Alex%20Evenings?id=157 I haven’t tried any of these pants but it looks like this brand has a wide assortment of evening pants in both regular and petite sizes. Prices are reasonable which would allow you to spend more on a top. They also are something that might be good to have in the closet for future occasions.
Cocktail Plus sounds like a step up from cocktail but not formal or black tie. So, I’d think cocktail with a little bling (since you said you were OK with a little bling). If you prefer to wear pants, I’d definitely stick with pants. Anything posted here thus far should work. It also sounds like you can look on Macys and/or Nordstroms websites (or whatever store is local to you for easy returns if you don’t want to ship back). I think these pre-assembled outfits work well for this situation–you don’t have to wonder if things “match” and don’t have to shop for multiple pieces – they all come together and the flowy look of these outfits seem very appropriate for a Malibu wedding.
I think this is groovy:
But you might get cold, and I’m not sure how a wrap would look with it. I just like it. You could put it with any kind of black pants you want.
I like this, too. I think it’s timeless and classic, but you may not want to be in all black.
https://www.dillards.com/p/calvin-klein-velvet-v-neck-side-tie-long-sleeve-jumpsuit/509698887
What about this? It comes in many colors.
Or this?
I like the two Calvin Klein jumpsuits but all black is probably out. I came across that Kay Unger jumpsuit/gown in my searching and I bookmarked it. Not sure I’d look good in it but I’d like to try it on and see.
My trick - pick the shoes you want to wear, then go shopping with them when you pick your outfit.
And as for shoes, check on whether the venue is on grass. If so, spiky heels are not good.
Don’t worry, my 68-year-old arthritic feet would never tolerate spiky heels. 
These days I favor wedge sandals. Some would not be dressy enough (enough long dress), but these are pretty - https://www.dsw.com/en/us/product/new-york-transit-funtastic-wedge-sandal/458931?activeColor=050&size=7
or many other examples
dsw.com/en/us/category/womens-mid-heel-2and188-3-wedge-sandals-size-7/N-1z141jrZ1z12dlbZ1z13vnlZ1z128ugZ1z141juZ1z128ry