My opinion matters not on lower back tattoos. However, I do think you are on the right track for giving yourself rewards for each weight loss goal you hit. What I tell people is to note your final weight you desire to be (Long Term Goal/Final Weight), and then to set smaller goals in between that are about 10-20 lbs for each short term goal. That way you are getting more of that immediate gratification instead of having to wait 6-12 months. Makes everything a lot easier, and less disappointing. For each short term goal, give yourself a reward/gift (i.e. your lower back tattoo). I hope you stick with this. I am very proud of you for being so open & adamant about your weight loss plans, and I just know you will be so happy with your end results!