Ugh body pillows...they make me feel claustrophobic. I bought a wedge pillow (Brentwood Home Zuma Therapeutic... https://www.amazon.com/dp/B00DTZVLTW?ref=ppx_pop_mob_ap_share) and sleep with this behind me, with a bunch of pillows stacked on top so I can sleep on my back on an incline. Way more comfortable and easier to get up and out of bed when I go pee 500 times per night.
I used this one. It was a life saver in the first 2 weeks because it hurt my stomach muscles to lay completely flat. With the wedge pillow, I could sleep with my upper body a little elevated and not stretch my stomach muscles or belly button incision. Later on I was able to flip it and use it as a back rest when I wasn't ready to sit at a 90 degree angle all day for work.
Get a wedge pillow from Amazon. They help ease the transition from dude sleeper (past me) to back sleeper (present me).
Brentwood Therapeutic Foam Bed Wedge Sleep Pillow - 100% Made in USA - CertiPUR-US - Washable Natural Bamboo Cover, 10" x 24" x 24" https://smile.amazon.com/dp/B00DTZVLTW/ref=cm_sw_r_cp_apa_i_5HD5DbG6QZ9VP
A pillow under your knees is key! It keeps pressure off your lower back and makes the transition easier. An alternative to pillows under your head is a wedge pillow for your upper body instead of sleeping on two pillows. I bought the 10" but in retrospect I should have bought the 7" one.
I LOVE my wedge pillow and still use it daily to watch TV in bed even over 8 months PO! Someone recommended it on this board in fact-- https://www.amazon.com/gp/product/B00DTZVLTW/ref=ppx\_yo\_dt\_b\_search\_asin\_title?ie=UTF8&psc=1
I'm sorry, I do not know how to find out if this is available in Japan, but here is the one I have (the 10" one) and it is well within your budget.
Everyone heals differently. I know a nurse and she said, "If you're taking pain killers when you're IN PAIN, you are HELPING your healing!" Do not feel like a baby at all.
I feel you on the lower back pain, I am a herniated disc recover-er. I used a wedge pillow behind me AND a bolster under my knees. Here and here Really helps relieve the stress on that lower back area. Or, many people here recommend a recliner of some sort. I had surgery in August and I'm still watching TV in bed with both my pillows!
I know you said moving around causes more pain, but really try to move. It will help the gas and the pain.
Don't get down on yourself. Before you know it you'll feel like a million bucks.