The exit row on the A319 is row 9 on pre-refurb aircraft (132 seats) and row 10 on post-refurb and ex-BMI aircraft (143/144 seats). If (and only if) you are on one of the remaining pre-refurb aircraft, the B seat in the first row of ET
may be blocked/converted. Check out
The BA Source for more accurate seat plans than BA/Seatguru.
About a third of all A319s are non-BMI non-refurbished aircraft - however by July your chances are slim to none. Not to mention that the particular aircraft type you will be travelling on could well change by then, and may well end up being an A320 or A321.