I highly recommend Wellage ampoules.

My skin has become super firm since I started using the Ellaju Real Hyaluronic Blue 100 Ampoule last year🤩 My skin type is combination (oily T-zone, dry cheeks), so I usually get sudden inner dryness in the summer and winter, but this ampoule really fixes that. However, it is a bit pricey, so I tried the 75ml size this time, and I think this one is better. Honestly, the volume is only about 25ml different, but the price difference is several thousand won or more, so it's a total bargain to stock up when Olive Young has a 1+1 sale.