AV+ fixed ISO vs Manual + Auto ISO using 550D? (Less light environment)

In my T2i/550D I shoot in Manual mode + Auto ISO except the time there is clearly abundant light present . At that time I use AV mode + ISO 100. If I'm shooting with flash I shoot fully Manual with Manual ISO.

My shooting pattern is focus using centre focus point and recomposing as I want it. In 550D only centre focus point is cross type.

Most of the time my shooting pattern end up with 80% M + auto ISO.. 15% Av + ISO 100 5% Fully Manual.

With M + Auto ISO I have this huge problem but I'm living with it..

Exposure is altered when recompose. It's spoil the exposure a bit (Though can be corrected in PP but in some condition it spoils the exposure more than 3 stops). AE lock doesn't work in Manual mode.

On AV + Manual ISO mode I found recomposing is possible after focus. It is no longer alter the Shutter speed when we recompose as It changes the ISO in M + Auto ISO.

So AV mode is better with fixed ISO than using M + Auto ISO for my centre screen focus followed by recomposing style of photography. But as you see when we want to make changes changing ISO in AV mode is harder than changing shutter speed in Manual mode. Because ISO is deep buried.

1) Any one Shooting using 550D with M + Auto ISO how do you conquer this big issue?

2) What is the solution? Am I missing some thing?
3) If I'm not missing some thing I have two choices
a) Use M + Auto ISO but instead of Centre focus point and recompose use closest focus point and reduce the recomposing. When I go out of ISO range it is easy to change the shutter speed than changing ISO in my next way (b). Also other focus points are not that good in grabbing focus as the centre does :(. I think that is the main reason they changed all focus points cross in present models of rebels.
b) Use AV + Manual ISO as it does not affect the exposure when recomposing so I can use the Centre focus point and recomposing, But when I end up out of shutter speed scenario I have to go through burred ISO and Change it.
a or b which do you recommend me to adopt for my 80% shooting scenario?