1x12 at 100watts reduces your options. Because the speaker is doing the job on its own you really want to be looking at speakers rated at 100watts minimum.
Check out a tonker if you want a brit/celestion kind of sound but i dont reckon it will be the best match for an amp like yours even tho the bands you like would have used brit speakers. Given that you are after marshall stack sounds from a fender ss amp you probably should just accept that if you cant copy the marshall stack sound, you can still make the most out of the amp you have. In that light, i reckon you should look at either a swamp thing or possibly a texas heat. A swamp thing is bigger sounding, clearer and more present with a more modern top end sizzle, but that may accentuate the buzzy frequencies in your SS amp. A texas heat is more of a classic sound with less efficiency and a darker top end. Its a sweet speaker but may not be agressive enough for you. Ill take a punt and recommend the swamp thing, but see if you can try before committing.
All 3 speakers (150watts) will have enough headroom to handle the job of being a lone driver with your amp. It just comes down to voicing and how they get along with your pedal driven dirt sounds.