A low branch does not exclude the pot option. Plastic nursery pots can be cut to any height to fit anywhere. I would still see that as an option now - remove the bottom and enough height from a suitable sized (diameter) pot and split one side so it can be fitted round the trunk and new root ball. Then you can remove the plastic (leave the current moss and new roots as they are) put the pot in place and fill with soil. That will allow more room for roots until you do the chop in spring. Some of the roots will grow into the pot underneath but they can be cut in spring when you do the chop.
Plastic pots are not the only possible material. Plastic mesh, garden edging and many other materials are suitable. Anything that is stiff enough to stand up and hold soil but bendy enough to wrap into a circle round the trunk is suitable to retain soil and can be trimmed to the desired height is suitable.
The branches on this one have been allowed to grow long, assuming to assist the layer so there's plenty of excess to cut when you remove the new tree. I'd be cutting back at least half of the current branches when removing a layer like this. half may not be half of every branch. If there are superfluous branches removing entire branches counts toward the total removal and 'half' is just a guideline. Prune whatever you feel comfortable with and the tree will compensate by growing a little less or growing more roots until it is balanced again.
Great result with the new roots so far. Looks promising for the next stages.
