For bras, if you have a Rigby & Peller store you can go to I'd recommend that. They have a wider range of brands and you can say your maximum price you can afford so they don't bring you the most expensive ones (some are a bit pricey).
I had a breast reduction & mastoplexy (uplift) abroad in my home country. Note that at your size, an uplift is necessary, it's not "just" a a reduction. Research the different types of breast surgery and risks e.g some keep the nipple attached with a blood supply to then be repositioned, others virtually cut it off and sew it back on. The bigger you are the more complex the surgery is. My surgeon was also clear he couldn't go as small as I wanted (C cup) due to my size and shape - I ended up an 32E (still a huge improvement though) and am currently a 36F due to lockdown weight gain.
I organised it all from the UK and chose a surgeon from 3 I shortlisted, going for the one that felt the most risk averse and nicest in terms of all the email contact, not the cheapest. I went to the consultation appointment on my arrival (with my sister as support), at that point either the surgeon or I could decide not to go ahead. He'd been clear he would not go ahead if he thought I wasn't suitable after all the pre surgery checks such as blood pressure etc. Ditto if I chickened out he was fine with that.
Had the surgery 3 days later, in hospital for 1 night, stayed with family for a few weeks taking it easy, checkups at 1 week post surgery and 2.5 weeks on day before I was due to fly back. Had to wear post surgery bra and compression stockings on plane and got lots of lectures about possible blood clots/DVT and signs to look for. Went to my UK GP for a check of the (dissolving) stitches a few weeks later and all was fine. Swelling took about a month to go down, scars were quite red and took about year to fade to skin tone, now you cannot tell unless peering very closely!
If you do consider going abroad, choose one with the qualifications and registered with a professional body for cosmetic surgeons, similar to in the UK (Royal College of Surgeons, British Association of Aesthetic Plastic Surgeons (BAAPS), the British Association of Plastic, Reconstructive and Aesthetic Surgeons (BAPRAS)) and only select surgeons from that list.
Look at their websites as you want someone whose done a lot of breast reductions (many specialise in certain types of cosmetic surgery) and email for ideas of prices and process. Take a friend with you -as you need someone who can stay with you after hospital discharge, in case you get an infection or become unwell. You need someone who can act fast to get help. Ask what the surgeon will do if there are complications and how costs for any rehospitalisation would be covered and if that would be part of the price of the surgery or extra. I was in a country that has reciprocal medical arrangements with UK but if you aren't, you'll need specialist travel insurance.
I totally understand your desperation but if you can do it in the UK on a payment plan/0% credit card I'd do that. I really only did it abroad as I had family there.