The outlook, in so far as it means anything, is for zero to +5°.
A lighter self-inflating mat, with perforated foam, will be marginal, so an extra closed cell foam mat underneath would be handy. Unperforated foam (giving a smooth outside surface) is a bit warmer, probably sufficiently so.
Down bags should mostly have an EU rating these days, and anything that says -5° or colder for "Comfort" should be OK. With synthetic bags, it's mostly still the old "season" ratings, which could mean either 3 or 4 depending on how warm you sleep. There's a fair difference between people - a bag that one person finds barely adequate at 5 or 6° could be too warm for another person at -5°. Generally women want a warmer bag than men do.
Down bags don't like getting properly wet, though a bit of dampness doesn't matter much. They are lighter and pack smaller for the same weight, and generally last quite a lot longer.
Synthetic bags are cheaper, and will give some warmth even if saturated. Repeated packing into a stuff bag will harm the ability to puff up properly, so they don't last as long if used regularly. The last one I had went from about zero to about +8 in about 18 months of being used most weekends plus maybe 4 or 5 weeks of holiday.
For a down bag, I'd suggest an Alpkit Skyehigh 700, or maybe 500 if you figure you won't be a cold sleeper.
For synthetic, Heltor's seems as good as anything.
The main point of a liner is to keep the bag clean so you don't have to wash it. They don't do very much for extra warmth.
A thought:
Could you just pinch the duvet off the bed? The one I use (double layer 9 + 4.5 = 13.5 tog down/feather) would probably be OK for me.