ASUS ROG Swift 27” 4K QD-OLED Gaming Monitor (PG27UCDM) - 240Hz, 0.03ms, Custom Heatsink, Neo Proximity Sensor, G-SYNC Compatible, 99% DCI-P3, True 10-bit color, DisplayPort 2.1a UHBR20, 3 yr warranty

That’s going to be an incredible upgrade. Either is good. The pixel density of 1080p at 24” is 92 pixels per inch. The pixel density of 4k at 27” is 163 PPI and at 32” 138ppi. Therefore I’d go with the 32” because it’s still sharper than your current experience with 24” 1080p and you get the 32” real estate. I’d consider these two monitors: » ASUS ROG Swift OLED PG32UCDMR – 32", 4K, QD‑OLED, 240 Hz. Flagship 4K gaming monitor with DP 2.1, KVM and great HDR. Some very solid panel protections. Builds on the legacy of the PG32UCDM. There is also a 27” version, the PG27UCDM » MSI MPG 322UR X24 - Another high-end, top of the line monitor. 4k with the latest generation Penta Tandem QD-OLED panel. 240hz, KVM, and all the connections you could desire…DP2.1, HDMI 2.1, and a 98W USB-C charger. These sell fast so get it if they’re available.

ASUS ROG Swift PG27UCDM, it's on sale right now too. Wish I waited 2 months and saved $200 https://www.amazon.com/ASUS-QD-OLED-Gaming-Monitor-PG27UCDM/dp/B0DM6SHQTN?th=1