First of all BaseProductId is not indexed in standard implementation of the accelerators elastic search. You have to index it via extending Litium.Accelerator.Search.ProductDocument (in Litium.Accelerator.Elasticsearch project) with BaseProductId and setting it while indexing. Do not forget rebuild the indices offline after your changes.
Then you can use something like following in order to search (see SearchQueryBilder of elastic saerchs ProductSearchServiceDecorator: