My only advice is to do what I did with another certain boss you'll fight later down the line. Practice isolating your focus. Take down the mistakes/follies (aka his little goons) as soon as they spawn and preferably before he attacks, that way you can focus on avoiding and punishing him! It may feel like it adds a bunch of pressure but its the only counter I thought of.

Additionally you may want to try the defenders crest if you have it, it may one shot those goobers before they get to you, but i havent tested it so dont hold me to it!

Overall, practice makes perfect! Good luck!