Hi, I also have a similar problem that the sitemap is too large but it does nto exceede 50,000 urls yet. The problem resolution should be the same to make multiple sitemaps.
I have one idea to simply change the name of the site map and set it to only add 10000 urls from the newest, but then there will be overlap urls in both sitemaps. Does anyone know if this is a problem or have a better idea.