Hi babawod, churidar or pyjama style salwar kameez are very fashionable (long line blouse often reaching below the knees, with trousers of a legging-type appearance). If you Google it, you will see what I mean. In my opinion, they are very elegant, beautiful and flattering.
When is the ceremony and what religion & occasion will the outfit be for? I am asking when, as if you have a few weeks or months to sort out an outfit, you could buy some material and take it to an Asian tailor and get it custom made (approx £25 depending on complexity of style and how embellished the fabric is). This is what most Asians do. Beware though, Ramadan is approaching and the tailors get very busy during this time.
Ebay is also a great option. A lot of sellers show photos of the finished product & you send them your measurements & they custom make it for you. You can also buy ready made suits and nearly new ones too.
Rupali is a good website with lots of sales and offers & they sell jewellery & accessories too.
Green Street, East London and Southall are good places for the whole outfit and accessories. With Ramadan starting in a couple of weeks, there will be lots of offers on clothes and fabric - more so in Green Street, as this has a higher population of Muslims than Southall. Unze is brilliant for shoes (they have an online shop too).
If it's for an Islamic Nikkah (wedding vowels with the Imam), I'd advise that you look for an outfit with long sleeves and try and do a hair style that won't flatten too much with the wearing of the dupatta (headscarf that comes with the suit). You can drape it around your neck most of the time, but when the Imam arrives & the vowels will be said, you'd need to cover your head (doesn't need to be worn tightly, but has to cover all hair).
Remember that you may need to remove your shoes in the home, depending on the religion & ceremony, so maybe don't make your shoes the 'star item!'
I'd avoid wearing white (associated with funerals). Some Asian brides do wear it now, so it'd avoid clashing with them (if it's a wedding ceremony). Potentially avoid red or pink as a main colour too if it's a wedding ceremony (lots of brides traditionally wear it).
Please let me know the answers to the above & I'll have a think & see if I can help you any more. I'm white & my DH is British Asian.