Having flown this yesterday I think the best economy seats here are row 10 aisle seats (first seats after Premium but row number depends on if its an 8 or 9) - I was lucky that the middle seat was empty and I was able to stretch my legs out into the aisle or even rest them on the partition in front which I am sure made it more comfortable as being able to move your legs makes the journey better when its longer.

After that I would say the aisle in front of the next exit row is great (24 on the 787-9) - there was even more room there than in front of 10 - but I am not clear if those seats are narrower as they are not main cabin extra unlike row 10.

Tomorrow I will be in the row behind that row 13 on the 787-9 and in the window seat as the aisle seats were taken so I will have less legs space and won’t be able to lift my legs up or get up as easily - also sure there is some poor person in the middle seat.