I may go the reverse route. Is the plus too big?
Apple "improve" 6+ to 6s+ on functionally, but weight and form factor actually taking a step back. 6s+ is both heavier and thinker than 6+. Not too much, but noticeable if you handle 6+ previously and transition to 6s+.
Look for 7 with overall weight reduce, thinner, and hopefully edge to edge screen which will allow narrower phone to be easier to handle with one hand. And if Apple could come up with new material change provide good grip without case, and also strong enough for drop/dent resistant on the case and screen (some kind of liquidmatel?), it will be like 1/2" reduction in width for naked 7 (or with very very thin case), compared with 6s+ with drop protection case, which is big different for one hand.