Hello Marge.
Sorry to read about your illness.
The weekly personal rate IP payment for an under 65 is €193.50 and the IB personal rate is €188 per week. Both are taxable, so changing from IB to IP won't affect your taxation situation.
Invalidity pension is not means tested so your medical situation and your PRSI contributions will qualify you for this. Unfortunately, it is very difficult to get the IP payment, the IP section is very slow in processing applications. I know someone whose Illness Benefit ceased in June 2012 and whose IP application has not been approved yet.
Unfortunately, when your illness benefit ceases, your IP won't kick in, and could/will take many months to be approved. You do have the option of applying to the local social protection offcer ( CWO) for a weekly supplementary payment, but this is means tested and you are getting €2k a month sick payment.
Fill in the app form with your employer details. You need to get your medical consultant to give you a detailed letter re your medical situation and send this in with the app form. The social worker in your particular hospital will be able to help you with your application and may help to get on to the IP section on your behalf. You may need your local TD or councillor to intercede with the IP section to speed things up.