I think the seats you've got are fine. Avoiding 8DG on the 77J is a good idea (a bit too much light/noise). For the same reason, some people prefer to avoid row 9 also. Other than that, all the J seats on the 77J are pretty much the same (just depends if you like a window). 11A & 12A are as good as any.

Please note it's really hard to talk b/w the D & G seats on the 77J so it makes sense to book two as you have done.

12JK will be fine on the 772.

Happy travels.