How to Search for Trademark Name Similarities Before Filing to amazon brand

I’m currently in the process of registering a trademark in the U.S. in order to later register it in amazon. , but I’ve hit a frustrating roadblock. My attorney charges $70 for each name clearance consultation, and so far, every name we’ve submitted has been rejected due to existing similarities. Needless to say, this is starting to add up quickly.

I want to get better at doing my own preliminary searches to identify potential conflicts before consulting my attorney. Does anyone have advice or tips on how to effectively search for similarities in perhaps a public database?

Any specific search strategies, filters, or third-party tools you recommend?

Thanks in advance for your help! I appreciate any insights to help avoid more costly rejections.