terrible skin disease (Erythema Centrifugum Annulare) and want to try Kefir- advice needed on what starter to buy

I've been to specialists for 30 years and no relief. The one thing that did help was a massive regimen of probiotic pills. Since, I've found Kefir and want to start making it myself.

So the questions for you kind folks-

1) I really need to use up this Amazon card. Is there a Go-To product available there with the most beneficial

2) I've been drinking this store bought LifeWay and it's pretty good! Can I use that as starter? I'll be doing this in the instantpot.

3) is there a definitive guide on using Lifeway or similar as a starter?

Many thanks! I'm committed to this!