If your lotion isn't thick enough, you can add a thickener like cetyl alcohol, behenyl alcohol, cetearyl alcohol, or stearic acid. (I can't link well on my phone, so please check out the links for each of these ingredients on the right hand side of the blog under bath & body guide to ingredients!) Start off with 3% in the heated oil phase of your lotion in place of 3% of any oil or butter and feel the difference! The most common of these are cetyl alcohol and stearic acid. They are quite inexpensive and have long shelf lives, and I think every good workshop has some of each in at least a small quantity.
For the most part, when you see a recipe with one of these thickeners you can substitute one for the other at the same percentage. There will be some difference in skin feel if you substitute behenyl for cetyl - behenyl is drier feeling - or cetearyl - which is waxier - for example, but 3% in the oil phase will offer thickening to even the wateriest lotion?
Want to know more? Do a search for these ingredients or the keywords "thicken lotion" and see what comes up!!