Hiya,
Because your hair is shoulder length- the fixed extensions will look great and very natural.. (any shorter than shoulder length and there are usually tell tale signs and the extensions are difficult to blend with your own hair)
I personally do not like the clip ins atall, only because i prefer to go to sleep and wake up with the hair as if it were my own, but if you only want them for special occasions then clips are the way to go..
It is so very important that you get the correct hair type to match your type. Also use human hair extensions - and if you are caucascian then make sure you only buy European/Russian/Georgian hair (RUSSIAN IS AMAZING QUALITY - BUT PRICEY)
If you are have dark, thick hair, then you should be using Indian hair, brazillian (curly) hair, or chinese hair - chinese bad quality in my experience.
If you have fine european hair then you should never have indian hair extensions, they will not blend atall and it will look very unnatural.
Greatlengths only use Indian hair which is why i wouldn't reccommend you go there if you have thin/fine blonde or brown hair.
If you want the best quality then you need to be buying "GRADE A" "REMY" "DOUBLE DRAWN" double drawn means all hairs are laying the same direction like the hair on our head, some cheap hair extensions will have some hairs lying root up, and some lying tip up. Be warned - if you buy the cheap "human hair" extensions for 40 pounds this will be the worst grade indian or chinese hair which has been chemically treated to give it a silky look, but will not keep this lustre and will tangle soon.
You could also consider buying "virgin" hair which has never been dyed.. if you are white then the most luxurious hair you can purchase would be virgin double drawn russian hair.
If you are darkskinned then most probably brazillian curly, or Grade A Indian Temple hair would be the best quality..
IF you live near london then go on gumtree.com and type in "hair extensions" It's great as you will find loads of mobile hair extensionists that will do it for a lot cheaper than the salons.. (be careful - loook for HABIA approved stylists, and ones with decents websites with before/after shots)/
To give you an idea..
(This is by the micro-ring method, arguably the best and safest method-no glue- this is also most expensive method)
European standard quality full Head hair extensions - 150-320 pounds
depending on length, and how thick your hair is.
Very good quality GRADE A European hair OR RUSSIAN HAIR full head 350- 700
Full Head Brazillian Curly 200-500
Full head Indian - 110 - 200
Full head Grade A Indian REMY 200 - 500
These prices are what mobile extensionists will charge, you can add atleast 300 or 400 pounds more for most salons..
Once you become a bit more knowledgable with hair extenisons you can even purchase wefts yourself from the net to save money and then take them to a stylist you can weft them in from 40 pounds..
Weft is different from the micro link method above - its NOT strand by strand - a small track is made on your head and the weft of hair sewn in..
There are also benefits with wefts- some people say its less damage, and there is more scope to create volume near the crown as hair is attached at root not at nape of neck.
If you wanna do this, go to www.russianhair.net... here you can buy top quality russian hand made wefts and the best thing is you can tailor make the size of them so they are the right size, and hold the right density of hair for your head..
You could get some guidance off a local stylist who agrees to put your weft in as to what size/how many to get or you can contact me.
Sorry hope i didnt bombard you with too much info.. anyway even if you dont live near london visit gumtree.com and look through the advertising hair extension stylists.. they explain all their methods and prices .. have fun.