Adding weight back on

I know this is a good situation to have. You have talked about going below your goal weight and see how you feel. My goal was 125 and I have drifted down to 120 lbs. I have a lot of wrinkled droopy skin and have started to look gaunt. I am 64 and prediabetic so I have to watch my intact of starchy veggies. I would like to gain a bit back? Any suggestions for adding foods back in that will put a few pounds back on? More fat? Add a snack? Thanks.