the best way to see if a companion dog is right for you is to become a foster mum for a dog shelter , you get to 'try out ' a few breeds and who knows the right dog may come into your life that way.
I did that with house bunnies, i wasn't sure i could cope with little furries hopping around my wheels, or what if..., but by fostering some i have realised that i could cope but only with small breeds, as larger rabbits are stronger than me and too heavy for me to pick up.
Fostering gives you peace of mind that if you don't bond then the animal can be returned. it also helps you to realise how much it will cost to feed, vet, entertain a pet without actually costing you anything during the fostering time. well i say nothing, if you are anything like me i treated them as i would my own pets and spoilt them rotten with toys, treats etc!
Whatever yoou chose, a dog is a long term commitment, it will need walking come hail rain or sunshine, so be prepared to be in the local park whatever the weather. dogs will chew your things and house if they are bored or teething. on the other hand they will give their life to protect you, give you a reason to get up, go out etc and will fill your heart with love.