You could try having two separate databases.
One is an OLTP (OnLine Transaction Processing) system which should be highly normalized so that the data model is highly correct. Report performance must not be an issue, and you would deal with non-reporting query performance with indexes/denormalization etc. on a case-by-case basis. The data model should try to match up very closely with the conceptual model.
The other is a Reports system which should pull data from the OLTP system periodically, and massage and rearrange that data in a way that makes report-generation easier and more performant. The data model should not try to match up too closely with the conceptual model. You should be able to regenerate all the data in the reporting database at any time from the data currently in the main database.