Privacy isn't great on Swiss J. There are no dividers or anything. The single seats are not so much better, so you can take the two middle seats without any problem.
The most "private" parts are rows 4 and 5 that are in a small separate part of the business class cabin just behind F.
Note that for being able to reserve single seats typically you need to have Senator/Gold status.
BTW, the 340 fleet is currently being renovated (due to be finished by year end I believe) the new seats are quite good, the old ones really show their age.