It would also be useful to be able to fly a 4 seater when the need arose.
As most 4 seaters are EASA aircraft, then a LAPL is the one to go for.
This will also have the advantage of being accepted all over Europe, should you want to go outside the UK.
MJ
Ps. BEagle beat me to it, but the LAPL should soon have the facility to add seaplane privileges, so this will probably be in place by the time you get your Licence.