DeGoogle Yourself

Others have already responded to your question more directly, but I also wanted to encourage a few other options for you and other people considering a bring-your-own-domain. You may have already navigated these, but I wanted to show how you are probably NOT overthinking it!

It will depend on your setup or chosen platform, but you don't necessarily need to use the 'recipient' addresses as your actual login address or 'real' mailbox address. As others described, you can have your kitchenware retailer and your government accounts send to their own dedicated addresses but have them land in the same mailbox. If you encounter a situation where you specifically need to send correspondence from that address, you can set that up later.

A connected but separate consideration is how you want your mailbox(es) to be organized. Do you want to read all of your email in the same mailbox, or do you want to separate human correspondence from services/machine mailings? Do you want to consolidate all of your Sent and Archived mail in the same mailbox, or separated? Do you want to have a completely isolated login address, or are you comfortable sharing that address with mailing use cases?

Again, some of these options may not be available with your given vendor, but it is possible with many of them. Your decisions will be based on your spam management goals, security goals/threat model, and your own workflow and email storage preferences. Have fun :)