What soothing serum should I try?

If you have sensitive skin, I think focus on barrier support and go easy on the acids. Aestura and Skin&Lab have pretty good products for barrier support.

I agree with @Choupette. Reduce products, especially if something like hyaluronic acid is stinging. Centella seems to me to "soothe" acne redness not redness from sensitivity. It's a KB ingredient learning curve! For me centella as a primary ingredient it is too much. Redness from sensitivity is the signal that your skin is broken and needs repair. Choupette mentioned Aestura, which is great. I'll go into a little more detail since it sounds you have normal skin and lots of barrier creams can be heavy or greasy. If you are experiencing sensitivty but your skin isn't like burnt toast yet (you can tolerate gentle cleansing and moisturizers without increasing redness or stinging.) 🧽 Etude SoonJung whip cleanser and toner for gentle cleaning and hydration without the intensity of a serum. They feature low ingredient lists that won't add to the product load on your skin. 🥣 Purito SEOUL - Oat PDRN Gentle Refining Toner (caveat, I have not tested this product yet. It's next to trial) However, depending on the condition of your skin, it might be a good product to layer in after using ETUDE SoonJung toner for a few weeks, especially if it feels like your skin needs some gentle clarifying. Avena Sativa (Oat) Seed Water is the first ingredient, which is excellent for soothing sensitivity and it's followed by some wonderful humectants. The problem is the presence of PDRN (not always well tolerated) and other ingredients like citric acid. Patch test on the edge of your face first. ❤️‍🩹 La Roche-Posey Cicaplast+ Baum is also fantastic for repairing the skin and decreasing irritation (zinc oxide is your friend!) and could be used as a night cream if it feels too heavy during the day. ❤️‍🩹 Isntree Mugwort Calming Cream is a fantastic "skip step" product. It adds hydration while providing that moisture barrier during the day without looking greasy. This is especially helpful when serums are too strong but toners don't provide enough hydration. Mugwort will address the redness -- and this is one of the few mugwort products that doesn't include niacinamide. It's there to baby your skin not to fight acne. 🥣 CYoung Hana AM/PM cream is another great "skip step" nutrient cream without harsh actives that can also be used during the day and is tolerated by a broad range of skin types. You can use this during the day and leave the heavier, oilier creams for the evening.

I like the skin1004 centella ampoule

I’ve also seen good things about the Anua 77 heartleaf toner