You point out some interesting research results.

However, the conundrum here is that if you seek friendships with people who are wealthier than you are, they will likely be spending more than you can spend, because they are able to do so without jeopardizing their financial well-being. This then puts you at risk of spending beyond your means if you feel like you have to do so in order to fit in.

The most important takeaway is that you should look for friends who, by virtue of who they are, call on you to be a better person, regardless of their relative wealth. These are people you should be comfortable around just being yourself, at whatever level of spending you can afford, whether they can afford less or far more than you can.