First off, let me say that I dared to choose lemon because my BMW is my second car. I have a Fiat Panda as a daily drive and only use the BMW for 'clean' trips
I have owned beige leather interiors before and have found the secret is to clean the seats (especially the driver's) before the dirt has chance to work its way into the leather. I usually give my seat a wipe-down every 500km or so, depending on use. Having tried several products over the years, I am very satisfied with
Mer cleaner &
Liquid Leather conditioner. They are both available on line from the UK. The cleaner is especially effective and the conditioner does actually restore that leather smell. I haven't actually tried them on my lemon interior yet, as the car is only 2 days old, but I have no doubt they will be effective.
Avoid dark jeans if possible, but don't become too paranoid. The real killer is leather jackets, because the oil in them comes off on the seats very quickly, especially if you use the heated seats function.