Which simple serum is best for older skin?

I'm curious to know, which simple serum would you recommend for older skin? As we age, our skin goes through various changes, including decreased collagen production and increased dryness. I'm looking for a product that can help address these concerns and leave my skin looking and feeling rejuvenated. Ideally, it would be something easy to incorporate into my daily routine, with minimal irritation or side effects. What are your thoughts on the best options available on the market?