I don't know how familiar you are with BA, but I just wanted to make sure you had correct expectations about Club Europe.

I personally think Club Europe is an excellent use of Avios due to the reward flight saver fares. £15 extra (£50 as opposed to £35 in economy) gets you lounge access, priority boarding, the middle seat blocked and better catering.

Depending on the aircraft you may or may not have a convertible seat. The seats are either the same as economy (non-convertible) or slightly wider than economy (convertible).

So don't expect much with the seat, but even though I get lounge access and priority boarding anyway due to being gold, I still think the little extra in cash + avios is worth the other benefits, particularly the middle seat block.

I'm not sure what seats are the best when travelling with an infant (I think row 1), but if you have questions on that front I'm sure someone will be able to help.