Hi, sorry to hear about your other guinea pig, that was a very impressive age,so you must be looking after them well.
You should be able to introduce another Pig quite easily.
Firstly i would house them seperatly but close enough that they can see each other, then each day let them play together preferably out of their cage, then you can see how they get on. if you think that they seem happy with each other start putting them in the cage together again supervised for a little while, if no fights occur then you could consider housing them together.
Would be adviseable to completely clean out the cage before putting them in together to prevent, territory disputes.
Hope all goes well.
Selena