We fitted engineered oak flooring at our last house that was a very old, damp house in the countryside. Advice was to use engineered as opposed to solid timber because of the damp conditions it would be exposed to.
I found that whilst there are masses of places online that will supply (mostly tiny) samples, this just confused me more as there were so many that were all slightly different - plus it's hard to tell from such small pieces.
In the end I was so bogged down and had enough different samples to cover the floor in a box room, lol that we went to a local independent flooring shop where we were able to take home large lengths to try out for colour etc. Their prices weren't the lowest, but customer service was excellent and we did get a good discount due to ordering such a huge quantity
We looked into the staining it yourself option, but I wasn't convinced - despite being veteran DIYers and house restorers - that we could achieve a consistency of colour. Otoh, DS has recently saved some cash by buying the untreated stuff, but they wanted a lighter colour which he achieved with oil/wax.