In Oxford to moor on the canal it is the stretch before Isis lock at Jerrico, but I think it is 2 days.
For water I would say fill in at Thrupp on the way down.
if you just want a couple of hours on the river go upstream from Sheepwash channel, you can turn before you get to the first lock if you don’t want to go through any lock, but if you turn below any Thames locks take care as it can be very shallow, and there is often a buoyed channel below locks.
If you can spend a bit more time continue up the river past Kings lock, where Dukes Cut joins, and there are mooring on fields at both sides of the river and that will give you more of the sense of what the upper Thames is like.