Toffeegirl
My heart aches for your pain. It is obviously with you every day, and you hold your sister in your heart.
THAT is where a memorial should be.
Not in a pile of rotten vegetation or plastic tat that over-dramatic individuals emote over for a week and then forget, or in competitive "you wiz took 2 soon" messages on FB - grief (as has been pointed out already) isn't a competition.
We found out that our local lollypop man had died because there were flowers beside his crossing area. Buckets were set up in local shops and at the schools to collect for the British Heart Foundation (I don't know how much was collected, but it will have been a LOT - he was a lovely man, and very popular).
On the day of his funeral, the cortege was driven past "his' schools, and the children and teachers lined the pavement to say goodbye. AT the end of the week the tributes were collected up and disposed of.
It was a lovely, fitting "good-bye", it gave children the opportunity to learn about loss in a safe environment, and the very fact that it wasn't prolonged, with morbid signs of death all over for weeks, meant that it had more impact - AND told them (implicitly) that it was alright to move on, and continue to enjoy life, because death is part of a very natural process.
It doesn't mean we forget the ones we loved, to that we wouldn't give our eye teeth to hug them once more- it means that we keep them in the place that they deserve - our hearts. I miss my mam and dad and grannie so much that even now it makes me weep (they all had very distressing deaths), but I know that none of them would want me or my children to be paralysed by grief, or to litter the countryside with junk!
There are many acceptable ways of providing a physical memorial, if that's what you feel you need. A number have been mentioned upthread. Explore one of these, and now that you aren't just remembering them, but aren't harming, and are often helping, others.
(I would say, though, as regards to "self-pity" city (what a vile remark!), there are some things that are so terrible - and so avoidable - that a permanent reminder is appropriate. The behaviour of the authorities during the disaster and its aftermath never should be forgotten. That's why MPs, etc don't like it - it's a reminder of THEIR inadequacy and lack of care. I'm glad that the memorial continues to rub their noses in it.)