How to join 2 sets of Prometheus metrics? - kubernetes

Question

AKS = 1.17.9
Prometheus = 2.16.0
kube-state-metrics = 1.8.0
My use case: I want to alert when 1 of my persistent volumes are not in a "Bound" phase and only when this falls within a predefined set of namespaces.
This got me to my first attempt at joining Prometheus metrics - so, please bear with me : )
I opted to use the following to obtain the pv phase:
kube_persistentvolume_status_phase{phase="Bound",job="kube-state-metrics"}
Renders:
kube_persistentvolume_status_phase{instance="10.147.5.110:8080",job="kube-state-metrics",persistentvolume="pvc-33197ae6-d42a-777e-b8ca-efbd66a8750d",phase="Bound"} 1
kube_persistentvolume_status_phase{instance="10.147.5.110:8080",job="kube-state-metrics",persistentvolume="pvc-165d5006-erd4-481e-8acc-eed4a04a3bce",phase="Bound"} 1
This worked well, except for the fact that it does not include the namespace.
So I managed to determine the persistentvolumeclaim namespaces with this:
kube_persistentvolumeclaim_info{namespace=~"monitoring|vault"}
Renders:
kube_persistentvolumeclaim_info{instance="10.147.5.110:8080",job="kube-state-metrics",namespace="vault",persistentvolumeclaim="vault-file",storageclass="default",volumename="pvc-33197ae6-d42a-777e-b8ca-efbd66a8750d"} 1
kube_persistentvolumeclaim_info{instance="10.147.5.110:8080",job="kube-state-metrics",namespace="monitoring",persistentvolumeclaim="prometheus-prometheus-db-prometheus-prometheus-0",storageclass="default",volumename="pvc-165d5006-erd4-481e-8acc-eed4a04a3bce"} 1
So my idea was to join these sets with the matching values in the following fields:
(kube_persistentvolume_status_phase)persistentvolume
on
(kube_persistentvolumeclaim_info)volumename  
BUT, if I understood it correctly you are only able to join two metrics sets on labels that match exactly (text and their values). I hence opted for the "instance" and "job" labels as these were common on both sides and matching. 
kube_persistentvolume_status_phase{phase!="Bound",job="kube-state-metrics"}  * on(instance,job) group_left(namespace) kube_persistentvolumeclaim_info{namespace=~"monitoring|vault"}
Renders:
Error executing query: found duplicate series for the match group {instance="10.147.5.110:8080" , job="kube-state-metrics"} on the right hand-side of the operation: [{__name__="kube_persistentvolumeclaim_info", instance="10.147.5.110:8080", job="kube-state-metrics", namespace="monitoring", persistentvolumeclaim="alertmanager-prometheusam-db-alertmanager-prometheusam-0", storageclass="default", volumename="pvc-b8406fb8-3262-7777-8da8-151815e05d75"}, {__name__="kube_persistentvolumeclaim_info", instance="10.147.5.110:8080", job="kube-state-metrics", namespace="vault", persistentvolumeclaim="vault-file", storageclass="default", volumename="pvc-33197ae6-d42a-777e-b8ca-efbd66a8750d"}];many-to-many matching not allowed: matching labels must be unique on one side
So in all fairness, the query does communicate well on what the problem is - so I attempted to solve this with the "ignoring" option - attempting to keep only the matching labels and values (instance and job) and "excluding/ignoring" the non-matching ones on both sides. This did not work either - resulting in a parsing error. Which in turn nudged me to take a step back and reassess what I am doing.
I am just a bit concerned that I am perhaps barking up the wrong tree here.
My question is: Is this at all possible and if so how? or is there perhaps another, more prudent way to achieve this?
Thanks in advance!