I am very sorry you lost your guinea pig. It is always so sad when your animals die. As of getting another friend for the other guinea pig, my answer is: When you get the other guinea pig, you should get a guinea pig of the same sex. When you introduce them, you must first put the new guinea pig in a separate cage next to your old one, for a day or so, so they can get used to each others smell. Then after a day, get both guinea pigs out on your floor (in an enclosed space) and watch them very carefully. If your older guinea pig starts to chase the new one or starts to bite it, then you should keep watching them and see if it keeps going. If the guinea starts to chase and hump the new one, you probably don't have to worry because it is normal that the old guinea pig wants to be dominant, this behavior should settle down after an hour or two but if the old guinea pig bites the new one, then you should put them together in a same cage and watch them, if the behavior continues, then certainly separate them. If the guinea pigs get on, then put them in the same cage and feed them at the same time, sit there and watch them. If the old guinea pigs make loud squealing noises and thumps her foot, and even tries to bite the other guinea pig, and if the older girl guinea pig does the same behavior when the new guinea pig is going for a drink, then you will have to separate them because your guinea pig wants to be the only guinea pig, and gets very possessive over her food and water. Also, if your guinea pig chases your new one around the cage, then separate them. Also, you should have the cage with the guinea pigs somewhere where you can hear what is going on, and if you hear squealing and running around the cage, then the guinea pigs are fighting and you should separate them. If they seem alright together, then you should keep an eye on them and make sure you don't hear bad noises in the cage. For a week, you should watch them while they are eating and check the new guinea pig for lumps, scabs, scratches, hair patches pulled out and red skin and lost condition. Also, you will have to get a very large cage because guinea pigs and other animals hate it when they are closed in and they need a lot of room to move, and if the cage is small, then the guinea pig is likely to attack the other one in a small cage.
I hope I helped and good luck to you and your guinea pigs.