Go ahead and take your temp, but you just make a note that it may not be totally accurate. Most of the time it will not make any difference (and certainly not at the part of yoru cycle you are in right now).
It doesn't matter what positiion you lay in for temping.
If your baby is only 14 months old and you will not be TTC for some time, please don't worry about your weight, wait till you're closer to your sway.