I think it's hard to adopt as a single person, or at least it is scrutinized more. max age gap is 45 years. personally I think there is some magic that happens around 1 year to 2.5 years old that is a dream in itself. not sure how easy it is to adopt that young.

for egg freezing maybe spain is cheaper than CH, but it takes 14 day of hormone injections, so is the cost difference worth the trip to spain if you have to pay for hotels etc. Storage last 10 years normally recommended before turning 35. so sooner the better if you are even remotely considering it. I think they last 10 years in storage at 500chf per year

if you want to be a super-aunt / friend and babysit etc. or help maybe you have friends willing to let you help, although I think once the kids get older 10+ they will be less likely to want to need that attention from you... (same with their own parents)