Given the ongoing issues with supply still, your choices might simply be down to what's available rather than what's "best" - unless you're prepared to be patient.

Thankfully there's not much genuinely bad gear out there these days.
If you're already OK for warmer weather then a good quality -1 to -8 degree C (comfort) down sleeping bag would be a sound investment, and allow you to continue doing overnight trips well into the shoulder seasons and possibly some light snow trips if you're keen. You can bolster a regular mid-insulated sleeping mat with an additional closed cell foam pad underneath for really cold conditions and snow, rather than invest in a separate winter-specific mat that will probably be too warm for summer use. Likewise a bivvy sack, emergency blanket/sack or parking your lower half into your hardshell jacket are all tricks to get more warmth out of your sleeping bag.
Sleeping systems are really personal so you're best bet is to check out every store you can, see what they have available there and then and try out as much as possible that suits your budget. Fit with sleeping bags is really person-specific; you want a snug fit for retaining warmth but if you've got broad shoulders etc. a lot of regular-sized bags might feel too constrained. Can be a fine balance.
To answer your second question: I use a Thermarest Xtherm MAX with a S2S Spark IV (-8 degree) for the cold half of the year, or an Enlightened Equipment Revelation 850fp +5 degree down quilt for the warmer half. I sleep warm generally, the Xtherm is a crazy warm mat (R6.9) that works well at elevation during summer (talking Tassie here) where I can make up the required warmth with clothing as need be, but often is a bit too much lower down and on the coast. Will then sub it out for my older Exped Synmat UL (R3.3) which is still pretty decent. Would eventually like to replace it with an Uberlite for both weight savings and I find the horizontal air chambers more comfortable, however Thermarests are crazy expensive/overpriced in this country, bit hard to recommend unless you're going to be using them regularly.
Hope that helps. Good luck with the shopping!