£399 is the regular upgrade price from WT+ to CW and £150 from WT to WT+. However if in WT you can't upgrade by two cabins, ie. from WT to CW. Also those people with connecting flights are not able to buy an upgrade at all, this is due to tax issues.

Although the F lounge is still at LGW be aware it has been made a little smaller in recent weeks so won't be quite as spacious as you remember it, but will have that same intimate, friendly appeal.

As for seating that will be your choice, but IIRC the front row of WT+ is immediately behind CW and the last row of CW has a bassinet seat. That may (or may not) mean an infant could be in those seats - this could be an issue for some though not all.