This is adapted from Behind Bars by Elaine Gould (a very comprehensive guide on notation):
A solid barline connects both staves at the beginning of a system. When the ossia stave begins mid-system at a barline, most editions do not include the initial barline through the cue stave: the dotted barline occupies only the space between the two staves.
When starting mid-bar, there is no connecting barline; it is free-floating.
So given your case, I would just use a short dotted line connecting the two staves in lieu of a measure line.
Also, I'm not sure I understand why you're using a double-bar there? Is there a tempo change? Also, you may want to consider putting the "Violin I - ossia" to the left of the staff instead of above.