Your question gives 2 things. First you have 4 databases on the same instance, and you use reporting services. You need to decide on which type of SQL Server you need. Here are some options:
1) SQL Server IaaS approach – If don’t want to change anything in how you use SQL Server, this is the best option. You will have full control over your Data and can use reporting service as needed
2) Azure SQL Single DB/ Elastic DB PaaS approach– If all of your DB’s have same usage, Azure SQL Single DB makes sense where each Database will have its own resources and if the usage is varied and different at different times, You can create a elastic pool. You may have to use different method or keep SSRS on-prem for reporting.
3) Azure SQL managed instance – This is closer to capabilities of On Prem Sql server and also provides you full range of PaaS capabilities but the SSRS also will not work here directly but have to use Cloud BI solutions.
So every approach has its advantages and disadvantages depending on work you want to do. Check what is needed most for your Data and what capabilities you can’t work without. Here is the complete list of comparison between two PaaS approaches and DB migration methods.
Hope this helps.
Thanks
Navtej S