What you have described is almost exactly CC BY 4.0, and saying so explicitly would remove the one question a commercial dev has to ask you before they can use this.
Free plus credit leaves three things unanswered, and people mostly will not message you to ask, they will just pick another pack. Whether commercial use is included. Whether they may modify the art. Whether they can ship it inside a game that is itself sold. CC BY 4.0 answers all three as yes with attribution, in wording people already recognise.
Second thing, and it costs nothing: put the licence in a LICENSE.txt inside the zip as well as in this post. The post does not travel with the files. Six months from now somebody has your folder sitting on a drive with no idea what the terms were, and the safe assumption they make is not to use it.