Item-based recommender using K-NN

I’m trying to build an item-based recommender using k-nn. I have a list of items, all of which have some properties (features) in common.

item    var_1      var_2    var_3        var_4          var_5
item_1  0.171547232  a      0.908855471  0.292061808    0.285678293
item_2  0.131694336  b      0.432665234  0.501300418    0.756824175
item_3  0.144318764  b      0.238752071  0.487600679    0.203133779
item_4  0.249241125  b      0.921229689  0.003638622    0.606875991
item_5  0.414306046  b      0.190824352  0.937412611    0.1789091
item_6  0.909501131  c      0.847112499  0.548322302    0.060136059
item_7  0.37469644   c      0.282628025  0.211128351    0.125910578
item_8  0.308634676  d      0.174650423  0.705026302    0.440098246
item_9  0.039294192  d      0.877086507  0.756817338    0.089838708
item_10 0.1641442    d      0.595879033  0.376224097    0.733153096 

Based on a random item input, I would like to find the top $10$ similar items using the k-nn algorithm and use them as a recommendation. However, I would also like to weight var_3 inversely proportional, hence when the value of var_3 is lower the item comes higher in the ranking of items suggested.

Do you have any suggestions on how to approach this?