I've had Maitai inserts for both B35 and B30, they're beautifully made and a pretty good fit. I don't use the one in my B30 often as I like her looking slouchy! But when I do it does help to make her look a lot more structured and does protect the interior if I want to carry things that may scratch the inside.
For storage I'd go with a bag pillow over bubble wrap. TPF rules mean I'm not allowed to recommend the brand I would like to, but lets just say there are pillows out there that are not made with polyester (plastic) and from the reviews are a very good fit for Birkins and Kellys.
They're also hand made with natural materials unlike a lot of the others available on Ebay, Etsy etc. which seem to be frequently a variation of the same imported pillow just with a different label!