Plain, sourced guides for the parts around your appointment: landing, getting across town, a place to rest, travel health cover and sending money. You book directly on the provider's own site.
Ask for the type and cost of the work in writing before you pay, and pay only against a detailed invoice. Germany's Foreign Office gives this advice for private care in Türkiye. Compare the total your clinic receives, not only the fee.
Entry rules depend on your nationality. British visitors need a passport valid for at least 150 days after arrival with one blank page. Germany's Foreign Office lists passport and ID card among accepted documents. Check with the Turkish consulate that the rules fit a treatment trip.
From Istanbul Airport (IST) you can take the M11 metro, a Havaist or İETT bus, or a transfer you booked ahead. A booked transfer meets you in arrivals, which helps if you land tired or with heavy bags.