Try FPosu I think it feels much more natural for you. FPosu is McOsu's FPS mode. You can set your Hfov 90 in game it gives you same cs go fov for 1280x960. You can download here. I show you how can you calculate your CS:GO sensitivity for FPosu in image. And I think osu is bad choice for warming your hands. I'm not aim expert but I think it makes bad habits on your aim. If u want to really warm your aim for CS:GO use any aim trainer in steam or play workshop maps. Sorry for my english.