I know exactly what you're dealing with. I used to switch between o2 and stepmania, and I've played some o2 while playing o!m as well. If your skin is wide, or is positioned in the middle of the screen, move it over/shrink it to the same size as o2jam is. The more similar you can make the interface, the less painful switching will be. You can also position the hit position into the same region as the o2jam hit position (the red bar at the bottom of the screen). The other thing is that you really just need to adjust to o!m's timing. You only have 23 plays on this account. Since o2jam has much more lenient timing than o!m does, it's going to take some time to adjust to o!m. You need to play a lot more. After 2 or 3 thousand plays you'll probably forget how hard this seemed.
Also, I suggest you don't play autoconverts. They have hard timing, and terrible patterns. Find some osu!mania specific maps to play here. It will pick ones with a difficulty you can play.
I have the exact opposite suggestion, play with a different skin, make it feel more like a different game, will adjust better like that. I'm switching between like 5 different vertical scrolling music games and on each one my skin has different widths/heights/colors, and this just helped me adapt faster when switching between them.
I managed to adjust from FtB by simply playing. Although the basic skin will really suck, get a skin that you might be more comfortable with. As for me, since I played o2jam and DJMAX a long time ago, I use a modified o2jam skin. Makes reading notes and timing easier. After nailing the skin, keep playing to get used to the strict judgment this game mode has.
Switching from o2 to lr2 and vice versa I dont have much problem, a little warmup session and I'm good to go. But switching to osu? fffffffffff. I FC stuff with Ds and it takes a week or two to start S'ing again though still having a bad max ratio, and the worst part is I'm not kidding at all.
I pretty sure the biggest issue is how you can't adjust your offset in osu. Note by offset I'm not referring to offsync. Offset will add or subtract xx-ms to your hits while offsync adds xx-ms to your audio.
There is however a pretty ghetto way of adding offset in osu and it's making your judgeline invisible and moving it around.
Thanks everyone for the reply/suggestion!! I'm getting used to it now. The only hurdle that i have to pass now is the slow jam which proves to be quite problematic (slow jam is much more lenient in o2jam i must say)