It depends a bit on if it is implanted across the os (mouth of the cervix) or just overhanging. Either way it will have to have moved at least 3cm from the os before they would consider anything other than a c-section so it is good you are already digesting that. This would normally be planned for 37-38 weeks (if no bleeding) to avoid you going into labour. The placenta at the back has slight pros and cons, it is a bit less likely to move away as there is less stretch at the back than the front in the later stages (spine etc), but is better for a section as there is less risk of cutting into the placenta.
I think in most places they don't 'diagnose' placenta previa until your repeat scan at 28/32 weeks. I think this is because most 80% + move by then. Think of blowing up a balloon with a circle next to the knot, as you blow it up it will stretch away. However, if the circle is pulled into or around the knot it is unlikely to move as it is anchored around it. For this reason I would assume that in your case it is unlikely to move and behave as though you are a bleeding risk and read up on your options later. I found the RCOG (Royal college of obstetricians and gynaecologists) guidelines useful. There is information for patients but also the green top guidelines which is for clinicians. For me this was useful as it also gave links to the evidence base for each risk/recomendation. Don't read it if reading about risk would panic you, as I said it is written for clinicians. For me it helped me make informed choices.
As I understand it, the muscle structure in the lower uterus is different and especially when things begin ripening you are more likely to get bleeding due to the placenta pulling or detaching. This is why I would do everything you can to avoid this and buy as much time as you can with baby inside. As others have said I would avoid sex, horse riding, nipple stimulation etc. I would also avoid being on my own incase of s big bleed. The other thing I would want to be on top of is iron levels. Discuss yours with your midwife, but even if you don't class as anaemic yet, you can buy sachets of iron water that are safe for pregnancy. Drink one a day with fruit juice (vit c aids iron absorption).
I would read up on options such as steroids to mature babies lungs, and the possible issues with a c section, and an early baby. Again don't if it will panic you, for me it made me feel in control to have already considered issues when faced with making decisions.
I would also think about having a hospital bag packed at some point, although now may be too soon.
I made it to 35 weeks and had an EMCS due to a big bleed. I lost a lot of blood. It wasn't too stressful as I was prepared that it may happen, but I wish I had been more prepared to have an early baby who needed more TLC.
Good luck and I really hope your pregnancy goes well. Please don't worry too much, they will look after you very carefully if it hasn't moved at 28 weeks. I am not medical so this is just my understanding from my reading and experience.