What a relief to see that strong heartbeat and a baby measuring right on track, those are genuinely good signs, and I can hear how much more reassured you feel compared to last time. The nausea without bleeding is actually a positive shift, and your hCG must be doing well if everything's progressing this nicely at 6 weeks.
That said, I'll be honest: a few mums I know who've been through miscarriage before mentioned that the anxiety doesn't always ease until around 8-10 weeks, because they know statistically the riskier window is right where you are now. It's not meant to scare you, quite the opposite. It means getting another scan in a couple of weeks to confirm things are still moving beautifully can make a huge difference to your peace of mind. Some found that having therapy or even just talking it through with their partner when the worry creeps in helped more than anything else.
At 36, you're not in a different risk category, and honestly, carrying a pregnancy after loss takes real strength, be gentle with yourself over the next few weeks. Your doctor will want to keep a closer eye on things, which is exactly what you need right now.
Wishing you all the best with this pregnancy, those numbers and that heartbeat are looking good. Do check in with your specialist about the timing of your next scan and what milestones to watch for, just so you've got a clear plan ahead.