Just use a pillow under your butt. Also if you're like me and your pelvis is tilted/you have a retroverted uterus, it won't do much good. If you need any suggestions or info, let me know- I have two kids with my previous husband and have been TTC with my current husband for 3.5 years, so I know quite a bit. Good luck.

P.S.- try to orgasm during sex- it helps pull the sperm up towards your cervix.