I'm by no means a fan of Mongo, but the product has improved quite a lot over the years. Mongo now supports multi-document (and multi-node) transactions, joins

I'm by no means a fan of Mongo, but the product has improved quite a lot over the years. Mongo now supports multi-document (and multi-node) transactions, joins, and has a decent storage engine. So you might even have a chance of keeping your data actually consistent.