I assume you have a SmartThings/Aeotec hub since you previously had Zigbee sensors, but can you just confirm that and which model?
Option 1: Wait for Matter
First, I personally am putting off most device purchases right now, until matter is more widely deployed. That’s likely to give us a much larger selection of candidate devices by spring of 2023.
Just as one example, the Aqara sensors are a popular candidate choice because they are inexpensive with nice engineering, but they can be tricky to get to work well with smartthings. Once both companies have fully deployed their matter support, it is likely that you will be able to buy an inexpensive aqara hub (of a model that specifically supports matter), connect your sensors to that, then add the hub to your SmartThings account (similar to the process for adding a hue bridge now) and it will bring along many of its devices. No custom code required. In addition, it’s probable that the integration will be stable, reliable, local, and you’ll be able to get firmware updates. In other words, a better integration than we have today and one that’s easier to use.
Ikea and Tuya will probably have similar options if everybody’s plans go as expected.
So while there are sensors that you could buy today, I think if you can wait a few months, you’ll have more choices for less money and with better functionality. But that’s up to you.
Option 2: Don’t wait, and get Aeotec zigbee sensors now (the replacement for the SmartThings brand
Samsung announced about a year ago that they were no longer going to manufacture the home automation hardware. Their partner in the UK, EU, and North America is now Aeotec. Aeotec was already a major Z wave manufacturer, but this agreement gave them immediate licenses for a line of Zigbee devices. These are essentially the same ones that had the previous smartthings brand name on them, just in a new box with a new logo. These should all work the same way as your previous ones.
It’s possible that previously you didn’t have enough Zigbee repeaters on your Network, but we can talk about that separately. It’s just that that’s a frequent reason for unreliability.
Option 3: don’t wait, and get third-party brand sensors
You didn’t specify whether you want to continue with Zigbee, or whether z wave or even Wi-Fi would be an option.
For Zigbee, The budget brands like tuya (sold under many different brand names) and Aqara can usually be made to work, but can be a little flaky as I mentioned previously. You’ll find lots of threads in the forum about those.
Hue zigbee motion sensors are well-made and reliable, and can be used either with a hue bridge or paired directly to a SmartThing/Aeotec hub. But they are more expensive than the budget brands. The outdoor models are very good choice for outdoors, though.