What's a reasonable weight progression?

I bought a 35lb kettlebell last year and in the last two months have been extremely consistent with it. Im ready to move to a heavier bell and am wondering what weight to buy. My thought is the 20kg bell, but I'm trying to be economical and have some concern that perhaps that's not a significant enough jump for the cost.

Do you think maybe a bell a bit heavier than that would be advisable? Perhaps a second 35lb bell would be a good idea?

Would appreciate your feedback.