I've started played accordion and harmonica at the same time, the latter in a rack. The key thing is to maintain the same breath direction, i.e. push mean blow, pull means draw. If you have a Paddy Richter tuned harmonica, e.g. where the blow 3 hole has been raised a tone, then this alignment between bellows direction and harmonica breath direction is lost.
That said, Paddy Richter makes a lot of sense. You would want to be certain that you really couldn't manage it before trying the tuning you seem to be suggesting, which is to raise the 2 draw hole a tone. While this could be done in principle, the resulting instrument might be rather odd to play, as the interval between the two hole blow and draw would increase to a 4th, which could lead to strange problems.
Retuning harmonica reeds is commonly done with plenty of online assistance, e.g.
https://youtu.be/pfC9OPmhyuUI'm mostly a harmonica player, so my solution for combined harmonica/accordion playing is to use a regular harmonica, and bend the 3 hole draw note when needed. This maintains the correct breath position, and works for me at least. You can see my efforts in this regard at
https://youtu.be/KYhG5FnjRGA
