One way to attach a floor joist at the wall to a post and not create a big joinery problem is to make the floor joist a "slide-in" joist.
That is you raise the frame and afterwards you slide in the joist from the outside before the siding is attached.
This joist can be somewhat smaller then the joist in the middle as it will not hold up as much as the others. It will be somewhat supported by the siding being nailed to it.
To make the joint not show (from the inside), a simple notch can be cut on the side of the post, large enough to hold the load and it could look like this: