Having attracted several responses with my original post I think it is time
that I thanked everyone, so ... Thanks!

All your comments have been well received. Here is a bit of personal
feedback:

I shall certainly be going to "sit in" some kayaks in the coming weeks, as
Peter, and particularly Charlie has urged me to do. I had already done
what they advised re getting a good paddle, before I posted - I bought a
Lendal Kinetic Touring (2 piece, 215 cm, with variable joint) with a
kinked carbon-fibre shaft and nylon blades. It's a beaut.

I know I want a boat suitable for lazy recreational and modest touring use
(ie with storage facilities), but not a big capacity boat that has me
bobbing around on the top of waves when its storage holds are empty, due
to the fact that I weigh so little myself.

I am intrigued by the Cirrus suggestion from Allan and David but I would
prefer to see more images, technical/design info, supplier/pricing data
and users reviews on the net first, and I just can't find any
manaufacturer or retailer websites offering this.

I agree with Peter that the Valley Avocet RM offers a lot for someone with
my brief. In fact, I may eliminate the Vela from my list (and instead
include the Easky or Capella RM) because it is a composite and I think all
the evaluating I am doing here and elsewhere tells me a good plastic boat
would be more sensible than a composite for my first purchase, given some
of the inland settings in which I expect to paddle.

I'm pretty settled on the idea of a boat around 15' - 16' long to optimise
the tracking/maneouvrability issue. And I'm keener on a retractable skeg
model rather than a ruddered boat.

I realise I need to go for as narrow a boat as I can fit into comfortably
(to make the regular paddling angles as easy on my arms and shoulders as
possible).

I'm now mostly preoccupied with the question of pay off between initial
and secondary 'stability'. I don't want a flat bottomed boat of any
description, but I can see that a boat designed for hard-core sea kayaking
could be unnecessarily tippy on say a canal or lake.

I realise some of you might think I'm being too 'theoretical' and need to
get in a damn boat! But I am boating each week on a river or lake while
this thought process of mine is taking place. Plus, I like working things
out as well as I can before buying things.

So, that's where I've got to friends. By all means write more if you want,
as I would be keen to read your views. If not, Thanks as I said for your
contributions up till now.
:-)