What worked really well for us was making a special "quiet time bag" with various activities for her to do. I planned to rotate them to keep the interest up, though haven't been that great at doing so, but she seems to enjoy what's in there. Top hits are paper and stickers or sticker books (things like 'dress the teddy' etc), colouring book and crayons, lacing cards or beads, a small magnetic drawing board, some cards with pictures/numbers on, an Aquamagic colouring thing....and of course a load of books. Occasionally if I see something I think she'd enjoy when I'm out shopping I will add it into the bag and then it's exciting for her to find out what's in there (and encouragement to get her into her room lol!).
When she would still nap relatively often, I used to draw the curtains and make it dimly lit (though light enough to see) so that she would be likely to doze off if needed. I don't bother so much now but sometimes she asks. I have wondered about getting a small radio/CD player for some music or stories as she gets older but haven't done so yet. I think M has a gro clock? Perhaps set it for 45 mins in the first instance and see how she goes?