self levelling is easy to do if you know what your doing you will need a mixer like what you would use for mixing up plaster a big bucket, Trowle And Stiple Roller. If you don't own these tools then you will have to hire or pay for them. The floor must be dry dust free and you must prime the floor before you latex it. The latex is made by simply adding the powder to the correct measured amount of water in your bucket and mixed thoroughly. Pour the mix over the floor surface and spread with a trowle then roll over the floor with stipple roller releasing air from the latex.repeat the process until your floor levels are the same. If you haven't done this before then you will probably save money by paying a professional to do this job you may make a complete mess which could cost you more in the long run.

Hi.

Although self levelling is a option you should actually look at the facts. depending on the products you use you could actually weaken the floor or in a worse case use a product stronger than the floor and it pulls tight and uplifts.
you need to check the newton meter of the floor this will let you know the strength. if you don't wish to go to this length use a low NM Smoothing compound.
It will save you a lot of money by getting the professionals in to do this correctly.