Just buy some resistence bands,the flat ones are the best,not the tube kind.
Try Iron woody or pullum sports,bands are great for pullups,just loop one end over the bar,then put the other end under your knee.These are great if you do not have a training partner.

Bands are also good for all your barbell exercises,just attach them to the bar,and your barbell takes on a new feel.Bands are worth adding to your home gym,because they have a feel of a pully machine.