Planting up a lily bowl

I have got a lily bowl, about 80cm diameter and 25cm deep in my garden. I plan to get a dwarf lily and a couple of other plants but there seems to be varied opinions on the net about whether to keep the plants in pots in the water or plant into aquatic compost in the bottom of the bowl. What do you think?
Also, does anyone have experience of buying pond plants online, as nowhere round here (Berwick-upon-Tweed) seems to have them.