Ahh winter camping with your wife. I used to do quite a bit with my wife and I learned a few things early on, which I'll share below. As for the tent, I'd look at what REI has to offer in the 4 season category, you should be able to find something in the $300-350 range. Winter tents are basically more robust [less mesh, higher-denier fabric, more poles]. Sleeping bags, I assume they're rated for the conditions you'll be in? If you're doing multi-day trips with down bags, make sure you have a vapor barrier liner [VBL] - one or two nights is no big deal. I never bothered with anything other than the sleeping bags and the therm-a-rests, but tossing-down a wool or synthetic blanket onto the bottom of the tent [with the therm-a-rests on top] would make for a cozy environment. Just remember that if you're camping on snow that blanket might be quite damp by morning due to condensation [that's why I never bothered].
Helpful tips for camping with your wife [from my own experience].
1] Women are more susceptible to cold than men. Make sure she has a warm down parka or similar that she can throw on during breaks and around camp.
2] If you're trudging around in the snow, make sure she has gators on to keep her feet dry and therefore warm.
3] Buy or even rent a damn warm sleeping bag. My wife has a -40C sleeping bag [nowhere near the temps we camp in, but it's comfortable for her].
4] A little pampering goes a long way to keeping her happy and itching to do more. When we get to our camping spot, we'd get the tent up fast and she'd get right into her sleeping bag to warm-up. I'd make her a Nalgene bottle full of hot water and she'd use it like a hot water bottle. I'd keep preparing/building the camp and securing our skis or snowshoes. Then I'd climb in and make her dinner. All easy to do and just keeps the experience positive.
5] Make sure she has decent gear i.e. make sure your gear and her gear are comparable. Our first "winter" trip together was around this time of year. There was 3-4' of snow down already. Her own gear was fine for 3 season, inadequate for 4. We had to invest heavily following that trip. If she's keen to get out a lot, make the investment.
Quirt mentioned below the Exped Down Mat 9 - I give the big 'ol +1 on that. They are very warm [R8 - thermal resistance - a therm-a-rest is around R1.5], but very very expensive. I bought one this year and I am looking forward to using it on snow. Maybe you could buy a used one. Have fun and keep the objectives reasonable.