It's really considerate of you to come on here posting asking how you can look after your significant other and make her feel a bit better.
The symptoms you are describing are unfortunately very normal - the first trimester especially can be brutal but some symptoms carry on and new ones appear as the pregnancy progresses. From my personal experiences, I've found both pregnancies very difficult and the 'glow' everyone talks about completely passed me by in my first pregnancy and doesn't seem to be arriving in my current pregnancy either!
I'm 19 weeks now and having my husband help with housework is great. Also little things like running a bath (not too hot), giving an impromptu foot rub, booking a nail appointment, just leaving her to have a long lie in etc have been lovely little touches. Things that will make your partner feel appreciated and supported - she's growing an actual human inside her body don't forget and it can really take its toll on a person.
It's also important to be a little extra tolerant and understanding. Pregnancy hormones are crazy and if she's snapping at you or getting angry, impatient etc it's likely to be that. Try not to take it too personal.
Not sure how many weeks she is but most people don't start buying baby things until 25 weeks minimum. You'll also probably find that that's something you'll both want to do together. It's one of the more exciting/ less stressful pre baby things to consider so neither of you will want to miss out on that experience. As a side note with that, i don't think anyone is suggesting you won't be equal parents but it's a simple fact that if your partner is on maternity leave while you are working for the first 6/9/12 months + then naturally it's your partner who will be doing more of the day to day baby care and walks with the pram etc at that time. Don't take it as a dig, it's just how it will be. Parenting, just like relationships, is rarely 50/50: at some points she will be doing a lot more than you but at other times you will be doing more. It's a partnership and you will settle into your routine and what works best for you all as a family.
Maybe instead of buying baby things, you could look to take her on a little shopping trip after the 12 week scan for some maternity clothes?
You're going to have the rest of your lives as a '3' or more so make this time about your partner and about you as a couple - maybe you could book a surprise baby moon?