Yep - as mentioned by @KarynJ and @SoldierCrab re 'reaching' .... NO HEAVY LIFTING either - that includes grandkids, dogs and washing!
Do you have a small 'oblong' pillow that you can use to support your injured side? It will be your godsend! Your Breast Care Nurse may be able to obtain a Zonta Pillow for you - but I just had a pillow left over from shoulder surgery. Initially, it is to support your arm as you will have to sleep on your back for a while & the arm sort of 'hangs there' & aches ..... so you rest the arm on the pillow, to support it. Then later, as you are able to roll onto your side, you swap the pillow to the other side, to support the arm at the same level as your hips - otherwise it just aches & you'll never get to sleep. It will become your best friend! I use mine even now, when I read in bed before lights out!
Talking of sleep ...... ask you GP (or surgeon) for some Temase now! The ones in the bottle that 'dissolve' ...... cos the one thing we ALL go thru is massive sleep disruption. It will give you about 4hr sleep - but hopefully, once you ARE asleep, you'll continue longer than 4hrs. Either our minds are too busy with all the thoughts going thru it - or it may be the medication/treatment that stuffs it up for us. They are NOT to be taken every night - but 'as required' for a decent night's sleep.
All going well, with a lumpectomy - you may not have drains depending on the surgery site (I didn't - my tumours were up behind the nipple.)
All the best xx