Sending good vibes your way! Here are some names that will hopefully help (that also sound particularly nice with Bugsy):
Jack Richmond (maybe after DH?)
I feel like you need something equally spunky and unique as Bugsy, which is hard because Bugsy is one of a kind. Do you have a particular name that is special to you like Bugsy was to your husband?
I think Ziggy could definitely work for you! I think it would stand on its own, or as a nn for Ignatius. If you love Ziggy, go for it! Bugsy and Ziggy are definitely cute together. Same style and you are not afraid to take a risk!
I really like Roscoe with Bugsy! or how about Guthrie?
I understand wanting to temper Bugsy's quirkiness, but I think you can't go too preppy or it really makes Bugsy look odd rather than quirky. Since it was such a meaningful choice for you that would be a great shame.
I like something brisk and cheerful:
Woodrow nn Woody
Napier (your maiden name, yes? Nn Nape or similar?)
Barton (quite like this for you-- phonetically similar to Marlon, and connects well to Bugsy via the B while being more grounded. unusual but not unfamiliar.also it was the middle name of Banjo Paterson, so a nice Aussie connection).