Thanks.
I've just got to find a sleeping bag that's not over 60 quid and I'm sorted
At that price point, for the summer, I think it's just a case of taking a punt on one of the established brands and seeing how you get on. As warm, lightweight and compact as you can get away with, it's always a bit of a balance between those and budget.
One of the best items I got a couple of years back was a cheap down jacket from Amazon to keep in my sleep kit just in case the temps drop. You may even be able to get a cheap down quilt from eBay, we got some down quilts for about £25 each a couple of years back and they are perfect for warm-weather camping.
My main advice though would be to try your full kit out before you go, a night in your garden or something. Nowt worse than having an uncomfortably cold night and then knowing you've got to do it again the next night.
To add a bit of insulation to the Numo you can use one of those mylar survival blankets, or cut a length of that thermal bubble wrap stuff you get for car windscreens and put it under the mat. Cheap and effective.

Rain covers are the worst, they just catch on things and flap around in the wind.