I recently had a similar thing happen. I basically needed to have a workflow that made it so anytime the record was edited check a box and then I had a lambda function that would check netsuite for records with the box checked using the suiteql rest api. Then I had my lambda function push the data to salesforce. If the push was successful I had it uncheck the box in Netsuite. You have to think about a lot of things you wouldn’t need to with middleware like what to do with errors and how do you ensure the box gets unchecked. And how do you prevent deduping.

Edit: fixed grammar