Kester cored solder has worked great for me, I don’t use any additional flux. That stuff is filled with it.
Just get this stuff and you should be set. I use the same gear
https://www.amazon.com/gp/product/B07PYFSCJ9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B00068IJQI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
That iron goes up to 500C and 120W. Included chisel tip works great. If you get the technique down, it can easily produce very good joints: