Advice on fusion surgery severe stenosis/listhesis

Hi, I am a 45 year old female due to have decompression and fusion (at L4/5) surgery for severe spinal stenosis and grade 1 spondylisthesis. My consultant suggested I should also have a fusion at L3/4 as this level would probably 'go' at some point in the future but he also said that this would 'bring more risk'. As I was already terrified of the risks associated with a one level fusion I said that I would just do L4/5 and see how it goes as this seems to be causing most of my symptoms at present. However as I wait for the surgery I am worried that I made the wrong choice. How much more risk am I really taking on by having fusion at two levels? Am I doomed to more surgery in a couple of year's time? I'm not sure I want to go through surgery again so soon and my employers are not likely to be thrilled either.  Any advice appreciated. Laura