Explanation
To send an email with personalized fields from multiple data extensions without coding experience, Northern Trail Outfitters should combine the data outside of Marketing Cloud and upload it into a sendable data extension. This will allow them to have all the required fields for personalization in one data source and avoid using complex scripting or queries to join and filter data from multiple data extensions.
Establishing data relationships and creating data filters would not help with personalization, as they are used for segmentation purposes. Creating SQL query activities would require coding skills and experience with SQL syntax. References:
https://help.salesforce.com/s/articleView?id=sf.mc_es_send_email_using_a_data_extension.htm&type=5